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This study is focused on developing visible-light sensitive anatase TiO 2 photocatalysts rather than the conventional UV-sensitive photocatalysts. We have adopted a surface modification technique using sodium borohydride (NaBH 4 ) chemical treatment. Thermal treatment under remarkably, favourable ambient air conditions were employed in this work instead of the previously reported inert gas or vacuum conditions, making it noteworthy. The synthesized surface-modified anatase TiO 2 is yellow in colour and has a crystalline core and disordered shell structure. The surface-modified sample was enriched with photocatalytically active shallow-traps due to the presence of Ti 3+ ions and singly ionized oxygen vacancies (V o + ). This surface-modified TiO 2 sample showed enhanced photodegradation of organic pollutants under visible light. The photocatalytic performances of the pristine and surface-modified samples were compared with the commercially available standard photocatalyst, Degussa P25. Notably, the surface-modified sample showed the highest degradation of Rhodamine B (RhB) dye, with a rate constant of 6.11 × 10 –3 min −1 . In contrast, the corresponding values for the pristine sample and Degussa P25 catalysts were only 4.15 × 10 –3 and 1.92 × 10 –3 min −1 , respectively. Our study summarises that surface modification is an effective strategy for developing efficient visible-light-sensitive TiO 2 photocatalysts. Graphical Abstract

In this letter, we report a new space charge suppression solution for polymer dielectrics by a manner of incorporating 2D Talc nanoclay particles to enhance shallow trap mediated charge transport. This approach was verified in both semi-crystalline cross-liked polyethylene (XLPE) and amorphous cross-linked ethylene propylene rubber (EPR), with large performance improvement independent of the crystalline morphology of polymers. The introduction of 2D Talc nanoclay modifies the distribution of the traps in polymer with enlarged number of shallow states, effectively increasing the charge carrier mobility while significantly reducing the macroscopic activation energies for XLPE from 0.88 to 0.66 eV and for EPR from 0.97 to 0.54 eV, as indicated by the quasi steady-state conduction measurement. The shallow trap mediated charge transport was further investigated by the Thermally Stimulated Depolarization Current (TSDC) measurement, confirming the decrease in the activation energy from 0.99 to 0.54 eV for XLPE and from 1.02 to 0.52 eV for EPR. The resulting higher mobility of charge carriers in the nanocomposite samples with 2D Talc nanoclay contributes to a notable suppression of the hetero-polar space charge, and consequently, a huge reduction of the local electric field enhancement, from 60 to 15% for XLPE and 31.5–11% for EPR, when tested at 50 °C with the presence of a thermal gradient. This trap-mediated charge transport study unveils a new approach for HVDC cabling with high scalability for future renewable energies.

The Al 2 O 3 nanoparticles (NPs) with favorable features were prepared in our lab to develop transformer oil/paper insulation system with better insulation performance. The nanofluids (NFs) were prepared with different shapes (nanorods, nanoplates), surface modifications (oleic acid, C 2 , C 18 ) and concentrations (0.6 g/L, 0.8 g/L, 1.2 g/L) of Al 2 O 3 NPs. The positive lightning impulse (LI) breakdown voltages (VBDs) of mineral oil were improved by 1.11 times with nanorod shape, oleic acid surface modification and 0.8 g/L concentration of NPs. The effects of Al 2 O 3 NPs with different gap distances on insulating properties of NFs under LI voltage were examined. It was noted that after Al 2 O 3 NPs suspension, the positive LI VBDs of transformer oil (TO/MO) were enhanced but the negative LI VBDs of were decreased. The significant improvement in insulating performance of NFs is interpreted in light of electron traps theory. It was found that suspended NPs can enhance the shallow trap desity. The generated electrons would lose their kinetic energy through repeatedly trapping and de-trapping process, leading to decline in elcetron mobility. The higher trap density of NPs will lower average energy, and lower mobility of electrons are obtained. The electrons with lower energy are easy to be captured by those molecules with high electron affinity, and be converted into negative space charges. These negative space charge decreases the electrical field strength at the front of positive streamer and therefore reduce the propagating velocity of positive streamer.

In this study, the relationship between thermal ageing and charge trapping properties of epoxy-based nanocomposites has been investigated. With ageing, any dielectric material undergoes thorough degradation. This degradation significantly affects the space charge accumulation and charge trapping behaviour of the dielectric, which are very important parameters for insulation health under high-voltage direct current (HVDC) environment. In this work, an improved model based on the isothermal relaxation current (IRC) has been developed to study the charge trapping behaviour of pure epoxy and epoxy alumina (Al2O3) nano-composites at different ageing conditions. A methodology based on polarisation–depolarisation current (PDC) measurements has been proposed to identify the current component due to a dipolar relaxation in measured total IRC. This will help to identify the trap distribution characteristics more accurately compared to conventional IRC measurements. It was experimentally observed that the addition of nanoparticles significantly reduces trapped charge formation and reduces thermal degradation. It is observed that aging leads to the generation of deeper traps, while the addition of Al2O3 nanoparticles mainly enhances the density of shallow traps. Results presented in this work indicate that epoxy–alumina nanocomposites are very much suitable in HVDC applications from the perspective of trapped charge accumulation.

Creeping flashover of mineral-oil-impregnated pressboard under impulse stress is a common insulating failure in oil-immersed transformers, arousing increasing attention. Recent studies have shown that the breakdown strength of transformer oil under positive lightning impulse voltage can be significantly improved through nanoparticles-based modification, and Fe3O4 has shown the best improvement in breakdown strength compared to other nanoparticles that have been used. This paper presents the creeping flashover characteristics of pure oil-impregnated pressboard (OIP) and nanofluid-impregnated pressboard (NIP) based on Fe3O4 nanoparticles under positive and negative lightning impulse voltages, respectively. It was found that NIP possessed higher resistance to creeping flashover than OIP. The relative permittivities of oil and oil-impregnated pressboard before and after nanoparticles-based modification were measured, and the results revealed that the addition of nanoparticles led to a better match in relative permittivity between oil and oil-impregnated pressboard, and a more uniform electric field distribution. Furthermore, the shallow trap density in NIP was obviously increased compared to that of OIP through the thermally stimulated depolarization current (TSDC), which promoted the dissipation of surface charges and weakened the distortion of the electric field. Therefore, the creeping flashover characteristics of oil-impregnated pressboard were greatly improved with Fe3O4 nanoparticles.

Quantum Dots of CdS^sub x^Se^sub 1-x^ embedded in borosilicate glass matrix have been grown using Double-Step annealing method. Optical characterization of the quantum dots has been done through the combinative analysis of optical absorption and photoluminescence spectroscopy at room temperature. Decreasing trend of photoluminescence intensity with aging has been observed and is attributed to trap elimination. The changes in particle size, size distribution, number of quantum dots, volume fraction, trap related phenomenon and Gibbs free energy of quantum dots, has been explained on the basis of the diffusion-controlled growth process, which continues with passage of time. For a typical case, it was found that after 24 months of aging, the average radii increased from 3.05 to 3.12 nm with the increase in number of quantum dots by 190% and the size-dispersion decreased from 10.8% to 9.9%. For this sample, the initial size range of the quantum dots was 2.85 to 3.18 nm. After that no significant change was found in these parameters for the next 12 months. This shows that the system attains almost a stable nature after 24 months of aging. It was also observed that the size-dispersion in quantum dots reduces with the increase in annealing duration, but at the cost of quantum confinement effect. Therefore, a trade off optimization has to be done between the size-dispersion and the quantum confinement.[PUBLICATION ABSTRACT]

Using a spherical concentric capacitor as a microspike model, the electric field distribution in a polymer dielectric material with shallow and deep electron traps is investigated. It is established that in the course of field emission from microspikes on the electrode and space charge accumulation on the traps, the values of coefficient of electric overstresses depend on temperature, injection barrier height, and trap concentration and depth in the polymer material. The behavior of this coefficient is characterized as a function of the mean field strength.

This chapter contains sections titled: Introduction Basic Aspects of the OSL Phenomenon OSL Readout Instrumentation Available OSL Readers Complementary Techniques Overview of OSL Materials

The transient dynamics of photocurrents for poly((4-diphenylamino)benzyl acrylate) (PDAA)-based photorefractive (PR) polymers sensitized with perylene bisimide derivative N,N′-diisopropylphenyl-1,6,7,12-tetrachloroperylene-3,4,9,10-tetracarboxyl bisimide (PBI) at various composition ratios were studied. The PR polymer included (4-(diphenylamino)phenyl)methanol (TPAOH) photoconductive plasticizer and (4-(azepan-1-yl)-benzylidene) malononitrile nonlinear optical dye as well, which are needed for inducing PR effects. All the photocurrents measured at 640 nm were well simulated by a two-trapping site model considering photocarrier generation and recombination processes of the charge transfer (CT) complex between PBI and PDAA. The process of photocurrent simulation allowed for analyses of the dependences of hole mobility, quantum efficiency (QE) of photocarrier generation, trapping parameters, and recombination coefficient on the PDAA/TPAOH content. Finally, the PDAA content dependences of the trapping and recombination properties were compared with those of the PR parameters of the optical diffraction efficiency, optical gain, and response time.

Hydrothermally synthesized ZnO photocatalysts with controlled cation deficiency were prepared to evaluate the role of Zn‐vacancy engineering in solar water splitting. Pristine ZnO (Zn) and Zn‐deficient ZnO were systematically characterized by structural, spectroscopic, and positron‐annihilation techniques. Zn1 preserved the wurtzite phase but exhibited vacancy‐induced lattice relaxation (100 d‐spacing: 0.285–0.286 nm; 002 d‐spacing: 0.266–0.268 nm) and crystallite refinement from 25.98 to 19.55 nm. Optical studies revealed bandgap narrowing from 3.14 to 2.97 eV and enhanced tail states (Urbach energy: 0.167–0.563 eV), indicative of improved visible‐light absorption. STEM–EDX confirmed Zn deficiency (Zn at.%: 43.06–33.90), accompanied by surface hydroxylation and electronic restructuring of the work function: 4.28–4.02 eV, while valence‐band maximum (VBM)/conductionband minima (CBM) positions remained favourable for H+ reduction. Charge‐carrier analysis showed suppressed near‐band‐edge recombination and extended lifetimes. Positron annihilation spectroscopy further evidenced increased vacancy trapping (τ2: 362–329 ps; I2: 70 to 74%). Zn1 demonstrates superior and nearly stoichiometric H2 and O2 evolution under sacrificial‐agent‐free UV irradiation (2 hr), with stable recyclability, confirming intrinsic enhancement of ZnO water splitting via Zn‐vacancy engineering. Controlled Zn vacancies introduce shallow acceptor states that induce valence‐band tailing and sub‐bandgap absorption, acting as transient traps to prolong carrier lifetime and suppress bulk recombination without creating dominant deep nonradiative centers. Simultaneously, Zn vacancies lower the work function and optimize surface adsorption energetics, facilitating charge extraction and interfacial transfer. Thus, an optimized Zn‐vacancy concentration ensures balanced light absorption, carrier dynamics, and surface kinetics in ZnO. Zinc vacancies in ZnO act as intrinsic acceptor‐type defects that create shallow trap states proximal to the valence band maximum. These defect‐induced states promote efficient separation and migration of photogenerated electron–hole pairs by suppressing rapid bulk recombination. As a result, the presence of zinc vacancies significantly enhances interfacial charge utilization, thereby improving the overall photocatalytic water‐splitting performance of ZnO‐based photocatalysts.