From conscious to unconscious and back. Remarks on Melanie Klein’s interpretation of Magic Word

The paper examines fluctuations between conscious and unconscious modes of mind functioning as outlined in Melanie Klein’s interpretation of Magic Word (Klein, 1929/1948), using the double lens of psychoanalytic and semiotic concepts of symbol. The study aims to explore the process of transformation that takes place in conscious and unconscious parts of the mind, when the mind overcomes maniac defences and is confronted with core depressive recognition: a truth about separateness of individual, and all anxieties it arouses. The examination of conscious aspects of depressive position will be performed through the prism of Charles Peirce (1998) semiotic, while unconscious content will be explored according to Melanie Klein psychoanalysis. The results of the study reveal, that employment of psychoanalytic and semiotic perspective simultaneously, when examining dynamics of psychic position, allows to break down the process to smaller, but still explorable sequences. Such approach allows not only to study most distinctive elements of the position but also to track dependencies that occur between them in time on both conscious and unconscious level. Moreover breaking down depressive dynamic to the smaller sequences facilitates more careful monitoring of the disturbing influence of unconscious to consciousness when psychotic response picks up. Similarly, sequential view enables more precise identification of the point when triangle space returns, and so facilitates analysis of conditions associated with that important change

Reactivity of sub 1 nm supported clusters: (TiO2)(n) clusters supported on rutile TiO2 (110)

Metal oxide clusters of sub-nm dimensions dispersed on a metal oxide support are an important class of catalytic materials for a number of key chemical reactions, showing enhanced reactivity over the corresponding bulk oxide. In this paper we present the results of a density functional theory study of small sub-nm TiO2 clusters, Ti2O4, Ti3O6 and Ti4O8 supported on the rutile (110) surface. We find that all three clusters adsorb strongly with adsorption energies ranging from -3 eV to -4.5 eV. The more stable adsorption structures show a larger number of new Ti-O bonds formed between the cluster and the surface. These new bonds increase the coordination of cluster Ti and O as well as surface oxygen, so that each has more neighbours. The electronic structure shows that the top of the valence band is made up of cluster derived states, while the conduction band is made up of Ti 3d states from the surface, resulting in a reduction of the effective band gap and spatial separation of electrons and holes after photon absorption, which shows their potential utility in photocatalysis. To examine reactivity, we study the formation of oxygen vacancies in the cluster-support system. The most stable oxygen vacancy sites on the cluster show formation energies that are significantly lower than in bulk TiO2, demonstrating the usefulness of this composite system for redox catalysis

SnO-nanocluster modified anatase TiO2 photocatalyst: exploiting the Sn(II) lone pair for a new photocatalyst material with visible light absorption and charge carrier separation

Modifying TiO2 to design new photocatalysts with visible light absorption and reduced charge carrier recombination for photocatalytic depollution or water splitting is a very active field. A promising approach is to deposit small nanoclusters of a metal oxide on a semiconducting oxide such as TiO2 or ZnGa2O4. In this paper we present a first principles density functional theory (DFT) investigation of a novel concept in photocatalyst materials design: Sn(II)O nanoclusters supported on TiO2 anatase (001) and demonstrate that the presence of the Sn(II)-O lone pair in the nanoclusters gives a new approach to engineering key properties for photocatalysis. The modification of anatase with Sn(II)O reduces the band gap over unmodified anatase, thus activating the material to visible light. This arises from the upwards shift of the valence band, due to the presence of the Sn 5s-O 2p lone pair in the nanocluster. Enhanced charge separation, which is key for photocatalytic efficiency, arises from the separation of electrons and holes onto the anatase surface and the Sn(II)O nanocluster. This work realises a new strategy of exploiting the lone pair in elements such as Sn to raise the VB edge of modified TiO2 and enhance charge separation in new photocatalyst materials

Charge compensation in trivalent cation doped bulk rutile TiO2

Doping of TiO2 is a very active field, with a particularly large effort expended using density functional theory (DFT) to model doped TiO2; this interest has arisen from the potential for doping to be used in tuning the band gap of TiO2 for photocatalytic applications. Doping is also of importance for modifying the reactivity of an oxide. Finally, dopants can also be unintentionally incorporated into an oxide during processing, giving unexpected electronic properties. To unravel properly how doping impacts on the properties of a metal oxide requires a modelling approach that can describe such systems consistently. Unfortunately, DFT, as used in the majority of studies, is not suitable for application here and in many cases cannot even yield a qualitatively consistent description. In this paper we investigate the doping of bulk rutile TiO2 with trivalent cations, Al, Ga and In, using DFT, DFT corrected for on-site Coulomb interactions (DFT + U, with U on oxygen 2p states) and hybrid DFT (the screened exchange HSE06 exchange correlation functional) in an effort to better understand the performance of DFT in describing such fundamental doping scenarios and to analyse the process of charge compensation with these dopants. With all dopants, DFT delocalizes the oxygen hole polaron that results from substitution of Ti with the lower valence cation. DFT also finds an undistorted geometry and does not produce the characteristic polaron state in the band gap. DFT + U and hybrid DFT both localize the polaron, and this is accompanied by a distortion to the structure around the oxygen hole site. DFT + U and HSE06 both give a polaron state in the band gap. The band gap underestimation present in DFT + U means that the offset of the gap state from both the valence and the conduction band cannot be properly described, while the hybrid DFT offsets should be correct. We have investigated dopant charge compensation by formation of oxygen vacancies. Due to the large number of calculations required, we use DFT + U for these studies. We find that the most stable oxygen vacancy site has either a very small positive formation energy or is negative, so under typical experimental conditions, anion vacancy formation will compensate for the dopant

Lead oxide-modified TiO2 photocatalyst: tuning light absorption and charge carrier separation by lead oxidation state

Modification of TiO2 with metal oxide nanoclusters such as FeOx, NiOx has been shown to be a promising approach to the design of new photocatalysts with visible light absorption and improved electron–hole separation. To study further the factors that determine the photocatalytic properties of structures of this type, we present in this paper a first principles density functional theory (DFT) investigation of TiO2 rutile(110) and anatase(001) modified with PbO and PbO2 nanoclusters, with Pb2+ and Pb4+ oxidation states. This allows us to unravel the effect of the Pb oxidation state on the photocatalytic properties of PbOx-modified TiO2. The nanoclusters adsorb strongly at all TiO2 surfaces, creating new Pb–O and Ti–O interfacial bonds. Modification with PbO and PbO2 nanoclusters introduces new states in the original band gap of rutile and anatase. However the oxidation state of Pb has a dramatic impact on the nature of the modifications of the band edges of TiO2 and on the electron–hole separation mechanism. PbO nanocluster modification leads to an upwards shift of the valence band which reduces the band gap and upon photoexcitation results in hole localisation on the PbO nanocluster and electron localisation on the surface. By contrast, for PbO2 nanocluster modification the hole will be localised on the TiO2 surface and the electron on the nanocluster, thus giving rise to two different band gap reduction and electron–hole separation mechanisms. We find no crystal structure sensitivity, with both rutile and anatase surfaces showing similar properties upon modification with PbOx. In summary the photocatalytic properties of heterostructures of TiO2 with oxide nanoclusters can be tuned by oxidation state of the modifying metal oxide, with the possibility of a reduced band gap causing visible light activation and a reduction in charge carrier recombination

Molecular metal oxide cluster-surface modified titanium (IV) dioxide photocatalysts

The surface modification of TiO2 with molecular sized metal oxide clusters has recently been shown to be a promising approach for providing TiO2 with visible-light activity and/or improved UV activity. This short review summarizes the effects of the surface modification of TiO2 with the oxides of iron and tin selected from d- and p-blocks, respectively, on the photocatalytic activity. Fe(acac)(3) and [Sn(acac)(2)]Cl-2 chemisorption on the TiO2 surface occurs by ligand-exchange and ion-exchange, respectively. Taking advantage of the strong adsorption, we formed extremely small metal oxide clusters on TiO2 by the chemisorption-calcination cycle (CCC) technique with their loading amount strictly controlled. The iron oxide surface modification of P-25 (anatase/rutile = 4: 1, w/w, Degussa) gives rise to a high level of visible-light activity and a concomitant increase in the UV-light activity for the degradation of model organic pollutants. On the other hand, only the UV-light activity is increased by the tin oxide surface modification of ST-01 (anatase, Ishihara Sangyo). This striking difference can be rationalized on the basis of the material characterization and DFT calculations, which show that FeOx surface modification of rutile leads to visible-light activity, while SnO2-modified anatase enhances only the UV-light activity. We propose the mechanisms behind the FeOx and SnO2 surface modification, where the surface-to-bulk and bulk-to-surface interfacial electron transfer are taken into account in the former and the latter, respectively.Research Front (Open Access

Engineering of metal oxide interfaces for renewable energy applications

Diminishing non-renewable energy resources and planet-wide de-pollution on our planet are among the major problems which mankind faces into the future. To solve these problems, renewable energy sources such as readily available and inexhaustible sunlight will have to be used. There are however no readily available photocatalysts that are photocatalytically active under visible light; it is well established that the band gap of the prototypical photocatalyst, titanium dioxide, is the UV region with the consequence that only 4% of sun light is utilized. For this reason, this PhD project focused on developing new materials, based on titanium dioxide, which can be used in visible light activated photocatalytic hydrogen production and destruction of pollutant molecules. The main goal of this project is to use simulations based on first principles to engineer and understand rationally, materials based on modifying TiO2 that will have the following properties: (1) a suitable band gap in order to increase the efficiency of visible light absorption, with a gap around 2 – 2.5 eV considered optimum. (2). The second key aspect in the photocatalytic process is electron and hole separation after photoexcitation, which enable oxidation/reduction reactions necessary to i.e. decompose pollutants. (3) Enhanced activity over unmodified TiO2. In this thesis I present results on new materials based on modifying TiO2 with supported metal oxide nanoclusters, from two classes, namely: transition metal oxides (Ti, Ni, Cu) and p-block metal oxides (Sn, Pb, Bi). We find that the deposited metal oxide nanoclusters are stable at rutile and anatase TiO2 surfaces and present an analysis of changes to the band gap of TiO2, identifying those modifiers that can change the band gap to the desirable range and the origin of this. A successful collaboration with experimental researchers in Japan confirms many of the simulation results where the origin of improved visible light photocatalytic activity of oxide nanocluster-modified TiO2 is now well understood. The work presented in this thesis, creates a road map for the design of materials with desired photocatalytic properties and contributes to better understanding these properties which are of great application in renewable energy utilization

A first principles investigation of Bi2O3-modified TiO2 for visible light activated photocatalysis: the role of TiO2 crystal form and the Bi3+ stereochemical lone pair

Modification of TiO2 with metal oxide nanoclusters is a novel strategy for the design of new photocatalysts with visible light activity. This paper presents a first principles density functional theory (DFT) analysis of the effect of modifying TiO2 rutile (110) and anatase (101) and (001) surfaces with Bi2O3 nanoclusters on the band gap and the nature of the photoexcited state. We show that band gap modifications over unmodified TiO2 depend on the crystal form: modifying rutile (110) results in new Bi2O3 derived states that shift the valence band upwards. On anatase surfaces, there is little effect due to modification with Bi2O3 nanoclusters, but an enhanced UV activity would be expected. Analysis of electron and hole localisation in a model photoexcited state shows enhanced charge separation in Bi2O3-modified rutile (110) but not in Bi2O3-modified anatase. The effect of the Bi3+ lone-pair on the properties of Bi2O3-modified TiO2 contrasts with SnO-modified TiO2, consistent with the weaker lone pair in Bi2O3 compared with SnO

Origin of the visible-light response of nickel(II) oxide cluster surface modified titanium(IV) dioxide

A number of NiO clusters have been formed on TiO2 (anatase/rutile = 4/1 w/w, P-25, Degussa) in a highly dispersed state (NiO/TiO2) by the chemisorption-calcination cycle technique. The NiO/TiO2 causes high visible-light activities for the degradations of 2-naphthol and p-cresol exceeding those of FeOx/TiO2 (Tada et al. Angew. Chem., Int. Ed. 2011, 50, 3501-3505). The main purpose of this study is to clarify the origin at an electronic level by the density functional simulation for NiO, Ni2O2, Ni3O3, and Ni4O4 clusters supported on TiO2 rutile (110) and anatase (001) surfaces. The clusters adsorb strongly on both rutile and anatase with adsorption energies ranging from -3.18 to -6.15 eV, creating new interfacial bonds between the clusters and both surfaces. On rutile, intermetallic Ni-Ti bonds facilitate stronger binding compared with anatase. The electronic structure shows that the top of the valence bands (VBs) of rutile and anatase arises from electronic states on the NiO cluster. On the other hand, the conduction band of rutile is from the Ti 3d states, whereas NiO cluster levels are generated near the conduction band minimum of anatase. This is in contrast to the SnO2/rutile TiO2 system, where the density of states near the conduction band minimum increases with the VB unmodified. In the NiO/TiO2 system, the band gaps of both rutile and anatase are narrowed by up to 0.8 eV compared with pristine TiO2, which pushes the photoactivity into the visible region. In view of the calculated electronic structure, we have attributed the enhanced photocataltyic activity both to the charge separation due to the excitation from the Ni 3d surface sub-band to the TiO2 conduction band and the action of the NiO species as a mediator for the electron transfer from the TiO2 conduction band to O-2

Metal oxide nanocluster-modified TiO2 as solar activated photocatalyst materials

In this review we describe our work on new TiO2 based photocatalysts. The key concept in our work is to form new composite structures by the modification of rutile and anatase TiO2 with nanoclusters of metal oxides and our density functional theory (DFT) level simulations are validated by experimental work synthesizing and characterizing surface-modified TiO2. We use DFT to show that nanoclusters of different metal oxides, TiO2, SnO/SnO2, PbO/PbO2, NiO and CuO can be adsorbed at rutile and anatase surfaces and can induce red shifts in the absorption edge to enable visible light absorption which is the first key requirement for a practical photocatalyst. We furthermore determine the origin of the red shift and discuss the factors influencing this shift and the fate of excited electrons and holes. For p-block metal oxides we show how the oxidation state of Sn and Pb can be used to tune both the magnitude of the red shift and also its mechanism. Finally, aiming to make our models more realistic, we present some new results on the stability of water at rutile and anatase surfaces and the effect of water on oxygen vacancy formation and on nanocluster modification. These nanocluster-modified TiO2 structures form the basis of a new class of photocatalysts which will be useful in oxidation reactions and with the suitable choice of nanocluster modifier can be applied to CO2 reduction