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Solvothermal crystallization is an adequate approach for preparing differently shaped TiO2 crystalline materials because it is highly sensitive to the synthesis parameters change. This study presents two sample series, one prepared from tetraisopropyl orthotitanate TTIP and one from tetrabutyl orthotitanate TBU. The influence of the applied temperature, different capping agents' amount, and the precursor volume ratio affected the measured characteristics (crystal phase composition, primary crystallity size, morphology, surface chemistry and optical properties). Although the samples revealed strong differences in crystal phase and size distribution, mostly spherical hierarchical morphology was achieved. The as-prepared samples were applied in photocatalytic processes to assess their efficiency under UV light and examine the influence of the structural features on the photocatalytic process. Not only the chosen precursor but the subtle changes in the listed parameters resulted in catalytical performance differences. Besides the crystal phase composition and the Ti3+ and Ti4+ species, it was found that organic surface particularities influenced the semiconductors’ photocatalytic performance.

The use of Azadirachta indica (A.I.) leaf extract to synthesize green photocatalysts for efficient separation of photogenerated charges has been a promising way to enhance the photocatalytic activity. Herein, we report the synthesis of green bismuth oxybromide/oxyiodide composites (G-BiOBrxI1−x) using A.I. leaf extract with effective size control, high specific surface area, and porosity. The A.I. leaf extract also acted as an excellent sensitizer that boosted the optical window of the G-BiOBrxI1−x photocatalysts. The as-prepared G-BiOBrxI1−x photocatalysts possessed three-dimensional (3-D) nanoplates like structure with successive modulation of the band gaps from 2.28 eV to 1.98 eV by varying the bromine/iodine (Br/I) ratio. Furthermore, the photocatalytic activity of the G-BiOBrxI1−x samples was measured and compared with the bismuth oxybromide/oxyiodide composite (C-BiOBr0.5I0.5) synthesized via conventional hydrolysis route (without the leaf extract). The G-BiOBrxI1−x photocatalysts degraded higher percentage of methyl orange (MO) and amoxicillin (AMX) than C-BiOBr0.5I0.5 under visible light irradiation. The superior photocatalytic efficiency was attributed to the multiple heterojunctions developed between BiOBr, BiOI, and electron-accepting π-conjugated system offered by leaf extract constituents, thereby facilitating the charge transfer process and effective separation of photogenerated charges.

Visible-light-driven photocatalysis using BiOX (Cl, Br and I) have gained tremendous interest due to their efficient performance, unique optical properties, and high chemical stability. In the present approach, the BiOX (X = Cl, Br and I) were synthesized by Azadirachta indica (A.I.) leaf extract assisted hydrolysis route followed by their immobilization on Alumina (Al2O3)-based ceramic fiber sheet as supporting material. The main objective of the present work was to eliminate the separation problem of the powder photocatalysts from the aqueous medium and evaluate their efficacy for the photocatalytic disintegration of organic contaminants in the long run. Furthermore, the as-prepared BiOX-ceramic fiber (CerF) samples i.e. BiOCl-CerF, BiOBr-CerF, and BiOI-CerF were characterized by scanning electron microscopy and BET-technique, which suggested that the BiOX were successfully embedded in the host matrix of ceramic fibers with an enhanced specific surface area. The photocatalytic activity of the BiOX-CerF samples was evaluated by varying operational parameters such as pH (2, 7 and 11), initial concentrations (20, 40 and 60 mg L−1) and in certain combinations. The results revealed that the higher pH value was more favorable for bisphenol A (BPA) and Ampicillin (AMP) degradation, while the MO was completely degraded at all pH range. Moreover, the stability test was performed and high stability of the immobilized samples was observed for five cycles without leaching out in the aqueous medium. The present study could offer new outcomes for advancing the large-scale applications of supported materials for environmental remediation.

In the present work Cu2O shape tailored microcrystals were obtained and investigated. The used shape-tailoring approach was based upon the variation of the starting precursor (copper(II) acetate and copper(II) chloride, the latter one being also much more cheaper and easily accessible), the synthesis temperature (60, 70 and 80 °C, respectively) and the shape tailoring agent applied (PVP vs. EDTA). It was found that cubic and polyhedral monodisperse microcrystals were obtained, which showed enhance visible light photocatalytic activity in the degradation of methyl orange. The activity was dependent of the formation of metallic Cu (the formed metallic nanoparticles were obtained when PVP was used), the microcrystals' size and morphology. The band-gap values were directly linkable to the obtained photocatalytic activity, while in the first derivative DRS spectra the electron transition contribution of facet (111) was also found, alongside of the polycrystalline Cu2O electron transition contribution. Also, the surface hydrophylicity played a crucial role in the determination of the photocatalytic properties as evidenced by IR measurements and DLS investigations as well.

Bismuthoxyhalides photocatalysts (BiOX, X = Cl, Br, I) were prepared using solvothermal crystallization method. The influence of the synthesis temperature (120 °C, 140 °C, 160 °C) and duration (3 h, 24 h, 48 h) on the structural (crystal size, phase composition etc.), morphological (crystal shape), optical (bandgap values) parameters and on the resulting photocatalytic activity were investigated. The samples were characterized by the means of X-ray diffractometry (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the synthesized materials was evaluated under visible- (≥ 400 nm) and UV light (≈ 365 nm) by degrading methyl orange and Rhodamine B (RhB). The results pointed out the importance of the crystallization temperature and duration in achieving the highest photocatalytic activity, showing that the lowest temperature and the shortest duration time resulted the highest removal yields. Furthermore, a possible degradation mechanism was elaborated based on a direct hole oxidation approach and the detected degradation intermediates.

It is widely accepted that the photocatalytic efficiency of TiO2 can be enhanced by modifying its surface with noble metal nanoparticles, such as Ag. On the surface of TiO2, Ag nanoparticles are exposed to rapid oxidation, resulting AgxO. Therefore, in the present work, the photocatalytic activities of TiO2 composites Ag nanoparticles were investigated. They consisted of commercial titanium dioxide mixtures (Aldrich anatase and rutile) in well-defined ratios and Ag nanoparticles, which were deposited on the surface of titania, with or without using a reducing agent. The transformation of Ag nanoparticles into AgO was monitored considering the anatase/rutile ratio of the reference catalyst(s). The effect of transformation on the photocatalytic activity of commercial TiO2 was also studied via the degradation of phenol and oxalic acid under UV light irradiation. It was concluded that the Ag nanoparticles deposited on the surface of rutile could increase the efficiency of charge separation. In the case of anatase, similar results were obtained for the as-formed amorphous AgO nanoparticles. The tertiary and quaternary composites generally exhibited higher photocatalytic efficiencies towards oxalic acid degradation than the corresponding commercial TiO2 mixtures. Ag nanoparticles were found to be unstable during the experiments as they transformed into Ag2O, which could transform back to Ag during the photocatalytic processes, under appropriate conditions. On the other hand, the stability of AgO was not affected during the aging period. Therefore, it was deduced that AgO is more stable on the surface of anatase compared to Ag and Ag2O nanoparticles deposited on the surface of rutile.

Nitrogen doping carbon nanotubes can enhance their beneficial physical and chemical properties, rendering them more desirable for various applications, e.g., in electronics. In this study, we used catalytic chemical vapor deposition to synthesize carbon na-no-tube forests on different substrates. The samples were prepared in the presence of compounds containing nitrogen (ammonia, acetonitrile, tripropylamine, and their mixture with acetone) that were introduced into the reactor by bubbling or injection. Of the two different nitrogen introduction methods, the direct injection of a liquid nitrogen precursor promoted the synthesis of bamboo-structured carbon nanotube forests more efficiently. It was found in the injection experiments that the amount of precursor affected the extent of nitrogen incorporation. The presence of various nitrogen species in CNTs was also identified, and the manner in which temperature and the presence of hydrogen both influence nitrogen incorporation into the carbon na-no-tubes was observed.

The inducement of plant leaf extracts for the synthesis of various nanostructures has intrigued researchers across the earth to explore the mechanisms of biologically active compounds present in the plants. Herein, a green modified hydrolysis route has been employed for the synthesis of bismuth oxychloride i.e. BiOCl-N, BiOCl-T and BiOCl-A using plant extracts of Azadirachta indica (Neem), Ocimum sanctum (Tulsi), and Saraca indica (Ashoka), and; simultaneously, without plant extract (BiOCl-C), respectively. The as-prepared samples were examined by several microscopic and spectroscopic techniques which revealed that the biosynthesized BiOCl attained certain favorable features such as hierarchical nano-flower morphology, higher porosity, higher specific surface area and narrower band gap compared to BiOCl-C. The degradation of methyl orange (MO) and bisphenol A (BPA) using biosynthesized BiOCl were improved by 21.5% within 90 min and 18.2% within 600 min under visible light irradiation, respectively. The photocurrent response, electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) studies indicated the effective inhibition of the electron-hole pair recombination and enhanced photocatalytic activity of the biosynthesized BiOCl.

In the present study hydrogen peroxide was applied during the synthesis of titanium dioxide (TiO2) photocatalysts to anchor peroxo groups onto the surface to enhance visible light excitability. The effect of changes in the pH value and crystallization temperature was investigated. As-prepared peroxo-titania were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), infrared spectroscopy (IR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity was investigated using phenol as model contaminant under visible light irradiation. IR and XPS measurements confirmed the presence of peroxo groups in the samples, moreover Raman and XPS measurements showed the formation of amorphous sodium titanate. Photocatalytic activity measurements pointed out, that most efficient as-prepared photocatalyst exceeded the photocatalytic performance of all reference materials. The cause of the enhanced photocatalytic activity was attributed to the enhanced visible light excitability and considerable amount of peroxo groups, which were not stable after the reusability experiments of the photocatalysts, suffering a redox reaction with the relatively high amount of Ti3+, resulting Ti4+ and surface OH groups. Therefore, the loss of peroxo groups and concomitantly photocatalytic activity was observed.

TiO2, Al2O3 and ZnO are grown by atomic layer deposition (ALD) at 80 °C on graphene oxide (GO), synthesized by the improved Hummers’ method. The preparation steps and the products are followed by FTIR, Raman, TG/DTA-MS, SEM-EDX, XRD and TEM-ED. Both Al2O3 and TiO2 grown with ALD are amorphous, while ZnO is crystalline. Through decomposing methylene orange by UV irradiation it is revealed that the GO itself is an active photocatalyst. The photocatalytic activity of the amorphous TiO2, deposited by low temperature ALD, is comparable to the crystalline ZnO layer, which is the best photocatalyst among the studied oxides. Al2O3 used as reference suppresses the photocatalytic performance of the GO by blocking its active surface sites.

The transformation and mineralization of monuron herbicide were investigated by heterogeneous photocatalysis, ozonation, and their combination (photocatalytic ozonation) at various ozone (O3) concentrations (0–20 mg dm‐3 in gas phase), using TiO2 in suspensions and in immobilized form. The applied AOPs were characterized by the transformation and mineralization rate of monuron, the concentration of dissolved O3, and the economic feasibility based on the values of Electrical Energy per Order related to the rate of decrease of monuron concentration and of the total organic carbon content. In the case of photocatalytic ozonation, the transformation and mineralization rate of monuron increased with the increase of O3 concentration. However, there was no significant synergistic effect. Electrical Energy per Order decreased with the increase of O3 concentration, and economical efficiency of the photocatalytic ozonation using TiO2 in suspensions highly exceed that of both ozonation and heterogeneous photocatalysis regarding the value determined for the decrease of total organic carbon content.

Orthorhombic molybdenum oxide (α-MoO3) samples were prepared via calcination. During this process, the ratio of the (0 4 0)/(1 1 0) or (0 4 0)/(0 2 1) crystallographic planes was fine-tuned by applying different calcination temperatures. Textural characterization of the samples was carried out to comprehend their differences in photocatalytic and adsorption applications. Except for methyl orange, all the tested dyes (methylene blue, crystal violet, malachite green, and rhodamine B) presented adsorption affinity towards α-MoO3. It was revealed that the presence of α-MoO3 significantly decreased the photocatalytic performance of TiO2 under UV light irradiation. With the growth of the (0 4 0) facet of α-MoO3, the photocatalytic activity increased while the adsorption affinity decreased for cationic dyes. It was found that the solubility of α-MoO3 depends on the proportional presence of the (0 4 0) facet, which determines both the adsorption and photocatalytic behaviors of the oxide. The solubility of α-MoO3 is reflected by the decreasing rate of solution pH, hence the adsorption can be measured accurately, but it varies according to the cationic dye structure. Using cationic dyes to assess the photocatalytic activity of α-MoO3 requires meticulous investigations since adsorption can be mistaken with photocatalytic activity: the adsorption rate depends on both adsorptive and adsorbent structures.

The “build-up” methodology, the importance of the order of the semiconductor layers in WO3‐TiO2/MWCNT composite materials was studied in terms of the applied synthesis pathway, morpho-structural parameters (mean crystallite size, crystal phase composition, morphology) and photocatalytic efficiency (using oxalic acid as model pollutant). The appearance of TiWOx phase in the composites contributed to the enhancement of the photocatalytic efficiencies, as different synthesis approaches led to different crystal phase compositions. Although, it was proven that a beneficial phase’s presence can be hindered if an excess of MWCNT or WO3 was applied. As the ratio of the mentioned materials was reduced, active composites were obtained, but the previously noticed TiWOx disappeared. Therefore, it was proven, that in the case of WO3-TiO2/MWCNT nanocomposite system several photocatalytic activity enhancement factors can be introduced, but not simultaneously (the disappearance of TiWOx at low MWCNT and WO3 contents and the appearance of highly crystalline anatase).

In the present work Bi2WO6 hierarchical flowers were obtained by hydrothermal crystallization and characterized by SEM, DRS, IR and XPS. The crystallization time and the influence of the crystal-shaping agents (Triton-X 100 and thiourea) was investigated on the UV and visible light degradation of Rhodamine – B and methyl orange (MO). It was found that after 15 h of hydrothermal crystallization an interesting structure appeared in the middle of the microflowers. The appearance of this morphological feature coincides with the appearance of Bi5+ and with the highest UV and Visible light activity. However, this material showed an outstanding activity when no thiourea was used. The latter contributed to the formation of surface anchored organics, which was proven to be detrimental for the sample obtained at longer crystallization times. These organic deposits can be removed partially, but it was not decisive concerning the photocatalytic activity.

Syntheses of highly ordered carbon nanotube (CNT) forests were studied from the aspect of the quality of CNTs and the properties of Fe-Co catalyst. CNT forests were grown by catalytic chemical vapor deposition. The amount of catalyst was varied in two ways: (1) catalyst layers with different nanostructure were produced with pulsed laser deposition by applying different argon pressures in the deposition chamber, and (2) compact catalyst layers were deposited with different thickness in 1–5 nm range. Our results show that both the nanostructure of the catalyst layer and the layer thickness have a significant role in the formation of catalytic particles, therefore also on the character of CNT growth.

In this work, we have prepared BiOI/CNT composites by hydrothermal method and studied the impact of CNT and hydrothermal treatment conditions (temperature and time) simultaneously on phenomena such as crystallization. The samples were studied using X-ray Diffraction (XRD), nitrogen sorption (Brunauer–Emmett–Teller (BET) specific surface areas), Scanning Electron Microscopy assisted with Energy Dispersive X-Ray spectroscopy (SEM-EDX), High Resolution Transmission Electron Microscopy (HRTEM), UV–vis Diffuse Reflectance spectroscopy (DRS), Raman spectroscopy and photoluminescence spectroscopy (PL). The different heat treatments applied and varied amount of CNT was found to have a profound effect on the structural, morphological, compositional and optical properties of the prepared composites. The distinguishable changes in the above-mentioned properties were clearly visible for the samples prepared at higher temperature and longer duration (150 °C, 6.30 h). Surprisingly, the presence of other phases of BiOI, such as Bi7O9I3, Bi4O5I2, Bi5O7I, also co-existed at the same time, although in low amount. Finally, for the study, the photocatalytic efficiency of the prepared samples was tested for phenol and RhB, as model pollutants, under visible light irradiation for 240 min and 120 min, respectively. The results revealed that the composites prepared at higher temperature with longer duration showed superior performance for the photodegradation of phenol and RhB. Additionally, the composites performed better than their respective reference samples in each case. Interestingly, the introduction of CNT promoted the crystallinity in the composites and promising results for the removal of phenol and RhB were achieved by the use of low power ordinary visible lamps.

The paper presents the influence of spherical Ag, Au nanoparticles (AgNS) and Au spherical nanocages (AuIND) on the photocatalytic properties (degradation of organic compounds and H 2 production) of commercial TiO 2 (Evonik Aeroxide P25, Aldrich anatase – AA and Aldrich rutile – AR). The resulted TiO 2 -based composites were characterized by different techniques, such as XRD (X-ray Diffraction), TEM (Transmission Electron Microscopy), DRS (Diffuse Reflectance Spectroscopy) and X-ray Fluorescence (XRF). For the synthesis of composites in situ (IS) and impregnation (IMP) procedures based on the chemical reduction method were used. The degradation of well-known model pollutants (oxalic acid and phenol) was carried out to find correlation between the applied synthesis procedure and the obtained photocatalytic activities. In all the cases oxalic acid was degraded efficiently by nearly all the composite materials (and showed superior activity compared to the base photocatalysts), while in the case of phenol the noble metal containing nanostructures were less efficient then the corresponding commercial TiO 2 . Furthermore, it was concluded that in the case of oxalic acid degradation, the nature of the used noble metals did not influence significantly the activity. From the chosen synthesis approaches IS method resulted the most efficient composites. When phenol was degraded, the formation of hydroxylated intermediates was favored instead of the phenol degradation. Under these circumstances, AA and AR based composites were the best when considering simultaneously both the intermediate formation and degradation efficiency values. For photocatalytic H 2 production the most efficient photocatalyst was the AuIND_P25_IS, which points out the effectiveness of the IS method.

The bioactive glasses doped with gold nanoparticles (AuNPs) are very attractive materials due to their potential in medical applications. In the present study Pluronic-nanogold hybrid nanoparticles were introduced during the sol-gel route of the SiO2-CaO-P2O5 glasses preparation. The obtained samples were characterized by UV-vis spectroscopy, X-ray diffraction, FT-IR spectroscopy, transmission electron and scanning electron microscopy and afterwards they were investigated in terms of bioactivity, protein adsorption and cells viability. The in vitro bioactivity assessment shows the increase of the number of agglomerated spherical shapes of apatite layers for all Au containing samples, but apatite like structure sizes are influenced by the AuNP content. Beside the spherical shapes, three-dimensional flower-like nanostructures were observed on the surface of the glass with 0.2mol% Au2O. Zeta potential and fluorescence spectroscopy measurements evidenced that the amount of serum albumin adsorbed onto the composites surface increases with the AuNP content. FT-IR measurements point out that the secondary structure of the adsorbed proteins presents few minor changes, indicating biocompatibility of the AuNP doped glasses. The good proliferation rate of Human keratinocytes cells obtained in the presence of samples with 0.15 and 0.2mol% Au2O is comparable with the values achieved from free AuNP, fact that proves the preservation of AuNP properties after their incorporation inside the bioactive glass matrices.

Shape-controlled synthesis of noble metal nanoparticles and their impact on the photocatalytic activity of semiconductor oxides is continuously gaining more and more attention. Hence, commercial titania-based TiO2-Pd nanocomposites were synthetized and characterized, using spherical and cubical Pd nanoparticles. The obtained photocatalysts were analyzed using optical (DRS) as well as morphological and structural (XRD, HR-TEM) methods in order to understand their properties. The effects of the Pd nanoparticles’ shape on different commercial titania-based catalysts were highlighted in terms of photocatalytic efficiencies toward model organic pollutants (phenol and oxalic acid), evolution of reaction intermediates (hydroquinone, pyrocatechol and resorcinol) and photocatalytic H2 production. It was found that both geometries (spherical, cubic) can enhance the activity of the base photocatalyst, although each Pd morphology modified the ratio of the primary degradation intermediates. Moreover, the photocatalytic hydrogen production of the spherical nanoparticles proved to be more efficient as the cubic ones. The observed activity differences were attributed to a possible change in the electron-transfer process, induced by the different Pd morphologies.

TiO 2 hollow structures (HS) were synthesized by carbon sphere template removal method. Nanometer sized carbon spheres (CS) were prepared by mild hydrothermal treatment of ordinary table sugar (sucrose). The size of these spheres can be controlled by the parameters of the hydrothermal treatment (e.g. time and pH). The obtained CSs were characterized by scanning electron microscopy (SEM), Raman spectroscopy, infrared spectroscopy (IR), X-ray diffraction (XRD) and thermogravimetry (TG). CSs were successfully coated with TiO 2 via sol–gel method. The phase composition of the TiO 2 hollow spheres were controlled by the annealing temperature during crystallization and CSs template removal. TiO 2 hollow structures (HSs) were characterized by SEM, XRD, Raman spectroscopy, TG and energy-dispersive X-ray spectroscopy (EDX). Photocatalytic performance of the TiO 2 HSs was evaluated by phenol degradation in a batch-type foam reactor under low powered UV‐A irradiation. The degradation reaction was followed by high‐performance liquid chromatography (HPLC) and total organic carbon (TOC) measurement techniques. Photocatalytic activity test results pointed out that increased rutile content up to a certain extent (resulting mixed phase anatase-rutile TiO 2 ) effects advantageously the photocatalytic performance of TiO 2 HSs and the unique morphology proved to enhance the photocatalytic activity (six times) as well as TOC removal efficiency (twelve times) compared to the sample which was prepared by the same method without the CSs.

Hydrogen peroxide was applied during the synthesis to enhance the visible light excitability of nanosized ( 2 -s. As-prepared photocatalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), infrared spectroscopy (IR), and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the catalysts were investigated by phenol, Rhodamine B dye and coumarin degradation under visible light irradiation. Evonik Aeroxide P25 TiO 2 and commercial rutile phase titanium dioxide were used as reference photocatalysts. First order derivative of DRS spectra showed enhanced visible light excitability in the case of Ti:H 2 O 2 = 1:2 ratio (applied during the synthesis). XPS measurements confirmed the formation of peroxo groups in this specific TiO 2 . Photocatalytic measurements pointed out that this TiO 2 had by far the best photocatalytic performance, exceeding the photocatalytic activity of Aeroxide P25 and commercial rutile as well. This activity gain was attributed to the presence of peroxo groups on the surface.

The carbon nanotubes (CNTs) play an important role in nanotechnology research today as they have the potential to be used in several areas. Environmental protection is highly discussed nowadays, which is why it is necessary to be able to produce CNT forests with less energy investment and simply, for these reasons we used the dip-coating layer construction method, which is a simple process. We also would like to simplify the production of CNT forests by changing several parameters used in the syntheses (concentration of ink, catalyst ratios, temperature, the effect of heat-treatment, hydrogen, and water vapor, reaction time, carbon source). For these reasons, this research uses a dip-coating method to form a catalyst layer on the surface of the substrate, as well as to investigate various parameters to produce CNT forests directly on the titanium substrate, as it is important today to use a conductive substrate.

Composite systems were prepared by doping NaYF4 (NYF) with lanthanide cations (Yb3+, Er3+, Tm3+), TiO2, and gold nanoparticles to exploit the light conversion properties of NYF and its possible impact on the photocatalytic activity of the composites. The composites were synthesized via solvothermal crystallization and the obtained structures were anatase TiO2, hexagonal NYF, and gold nanoparticles of 5–7 nm. The presence of NYF enhanced the photoactivity of TiO2 towards Rhodamine B degradation under UV irradiation, while it decreased its performance under visible light. The presence of Au was beneficial when visible light was applied for the degradation experiments. The reason behind the enhanced activity was the fluorescence of NYF at 400 nm that was the most intense for the composites that did not contain gold. The NYF-based samples also showed signs of up-conversion when 900 nm was the excitation light source, highlighting the potential of this material for photocatalytic applications that utilize the full (UV–IR) light spectrum.

The influence of a radical scavenger (tert-butanol (t-BuOH)) and two radical transfer materials (formic acid (HCOOH) and formate anion (HCOO−)) on the radical set during radiolysis of a simple model compound, phenol (PhOH, 1.0×10−4 mol L−1) is discussed in this study. PhOH solutions were irradiated with γ-rays, in the presence of 1.0×10−3, 5.0×10−2 and 5.0×10−1 mol L−1 t-BuOH, HCOOH or HCOONa under deoxygenated and O2-saturated reaction conditions. The rate of transformation of PhOH increased significantly in the presence of dissolved O2. The radical transfer or scavenger materials used reduced the rates of transformation of PhOH in O2-saturated solutions to a similar degree. The simultaneous presence of O2 and the organic additives in excess proportionally to PhOH results in the conversion of the radical set to less reactive intermediates (t-•OOBuOH, HO 2 • or O 2 • - ), which made minor contribution to the transformation of PhOH. Under oxygenated conditions, t-BuOH and HCOOH in low concentrations slightly promoted the degradation, as opposed to HCOO− which reduced it. However, using higher additive concentrations, their competitive reactions for the primary intermediates came into prominence, thus they reduced the efficiency of PhOH decomposition. HO 2 • and O 2 • - , and also the carbon-centred radicals formed (order of their reactivity t-•BuOH>•COOH> CO 2 • - ) have only a minor contribution to the degradation of PhOH, and the reactions of •OH+PhOH and eaq−+PhOH are the significant processes.

The nanostructured BiOI-Q-Ag composites were prepared by a quercetin-assisted hydrolysis route under varying concentrations of Ag. The samples were examined under microscopic and spectroscopic investigations, which revealed that the Ag nanoparticles (NPs) were efficiently loaded on the 3D BiOI-Q nanoflowers, and a higher density was observed with increasing amount of Ag. The photocatalytic activities of the as-synthesized BiOI-Q, BiOI-Q-Ag (1), BiOI-Q-Ag (2), and BiOI-Q-Ag (3) samples were examined for the methyl orange degradation (MO) and antibacterial activity against four different bacteria i.e. Bacillus pumilus, Acinetobacter baumanni, Staphylococcus aureus, and Pseudomonas aeruginosa under visible light irradiation (VLI). The BiOI-Q-Ag composites showed improved photocatalytic performances over BiOI-Q signifying the important role of the Ag amount and the optimized ratio was obtained at BiOI-Q-Ag (2). The enhancement in the visible light photocatalytic performance of the BiOI-Q-Ag composites could be attributed to the effective separation of the photogenerated electron-hole (e--h+) pairs at the multiple interfaces developed among BiOI, Ag and the quercetin, which facilitated the effective charge transfer. The trapping experiment suggested that the h+, .OH, and . O2− were the dominant active species in the photodegradation process. The electrochemical studies showed that the recombination of the photoinduced charges in the BiOI-Q-Ag (2) composite was inhibited strongly as compared to the BiOI-Q sample. The photocatalytic activity of the BiOI-Q-Ag (2) composite was maintained for the cycling experiments.

Titanium dioxide hollow spheres (TiO2-HSs) were fabricated by applying carbon spheres (CSs) as templates, which were eliminated by calcination. The most suitable TiO2 was selected and an attempt was made to further increase its photocatalytic activity via noble metal (Au and Pt, at 0.25 wt%) deposition. The photocatalytic efficiency was determined by the decomposition of phenol and oxalic acid under both UV-A and visible light irradiation. It was established, that both the unique morphology and the presence of noble metals contributed to the photocatalytic activity gain compared to the solid spherical reference. For the elucidation of the observed phenol degradation performance under UV-A light irradiation, new insights were proposed: within the TiO2 samples the ratio of HSs with enhanced light trapping properties were demonstrated, and the data was compared to the observed photocatalytic activities and a direct correlation was found.

AgI microcrystals are used as Ag nanoparticles’ source to avoid the transformation of silver into AgCl, whose presence can affect the materials’ biocompatibility. The AgI microcrystals are obtain by using solvothermal crystallization and then they are embedded into bioactive glass matrices using a sol-gel method. The influence of AgI concentration on the structural, morphological, bioactive and biocompatible properties of the composites is carefully analyzed. By using the above-mentioned approach, all the obtained samples are AgCl free. Furthermore, the sample with 0.1 mol% AgI shows the signature of mobile I− and Ag° metallic species that negatively affect the in vitro bioactivity. It is also demonstrated that the presence of Ag° metallic species restrained the keratinocytes cells viability. The composites with AgNPs and Ag2O species exhibited excellent bioactivity and good cell proliferation rate. A moderate antibacterial effect against Pseudomonas aeruginosa was also evidenced in the case of the composites with AgNPs content.

Bismuth oxybromide samples were synthesized using solvothermal crystallization and different additives (CTAB-cetyltrimethylammonium bromide, PVP–polyvinylpyrrolidone, SDS–sodium dodecyl sulfate, U–urea and TU–thiourea). The effect of the mentioned compounds was investigated through structural (crystallite size, crystal phase composition, etc.), morphological (crystal shape), optical (band gap energy) parameters, surface properties (surface oxidation states), and the resulting photocatalytic activity. It was found that the ratio of the (1 0 2)/(1 1 0) crystallographic planes, the presence of oxidized Bi4+ and Bi5+ species were responsible for the obtained photocatalytic activity. Moreover, a strong dependency was revealed between the surface tension of the shape tailoring agents and the overall morpho-structural parameters, pointing out the fact that the properties of the semiconductor can be more easily tuned using the surface tension modification as a tool.

In the present study, a 2D hollow-cylindrical activated carbon block (CB) has been converted into a potential photocatalyst by impregnating green bismuth oxyiodide (BiOI-G) synthesized via Azadirachta indica (A.I.) leaf extract mediated hydrolysis route in the activated carbon (AC) matrix (BiOI-G-CB). The as-obtained products were well-characterized and it was discovered that the BiOI-G nanoflowers were successfully embedded in the 2D CB’s matrix with homogeneous distribution. Furthermore, the density of BiOI-G embedded in the 2D CB structure was varied by adjusting its amount with the precursor in different ratios i.e. 0.1 wt%, 0.5 wt% and 1 wt%, respectively. The rationally designed BiOI-G-CB displayed a significant photocatalytic activity by degrading 94.1% and 91.8% ampicillin (AMP) and amoxicillin (AMX) within 300 min of visible light activity. The superior photocatalytic efficiency was credited to the multiple interfaces developed among activated carbon, BiOI-G and leaf extract, which facilitated the charge transfer process and effective separation of photogenerated charges.

Transformation of coumarin (COU) and coumarin-3-carboxylic acid (3-CCA), the formation of their fluorescent hydroxylated products, (7-hydroxy-coumarin (7-HO-COU) and 7-hydroxy-3-carboxycoumarinic acid (7-HO-3-CCA)) were investigated and compared using three different advanced oxidation processes: gamma radiolysis, VUV (172 nm) photolysis and heterogeneous photocatalysis (TiO2/UV (300–400 nm)). Beside •OH (hydroxyl radical), other reactive species: H• (H-atom, in VUV irradiated aqueous solution and in gamma radiolysis with low yield) and eaq− (hydrated electron, in gamma radiolysis) also contributed to the degradation. The reaction rate constants of COU and 3-CCA with each reactive species were determined via pulse radiolysis. The values obtained were: 6.88 × 109 and 4.9 × 109 with •OH; 2.5 × 109 and 1.3 × 109 with H•; 11.4 × 109 and 14.3 × 1010 mol−1 dm3 s−1 with eaq−, in the case of COU and 3-CCA, respectively. Based on the results of radiolysis it was suggested, that the formation of fluorescent products are initiated only by •OH. The effects of dissolved O2 and •OH scavengers (MeOH and t-BuOH) were also investigated. In radiolysis dissolved O2 increased the formation rate of fluorescent products. In VUV photolysis of COU and 3-CCA solutions the inhibition effect of alcohols was more pronounced in the presence of O2 than in its absence. In heterogeneous photocatalysis both MeOH and t-BuOH decreased the transformation rate of COU, while they had no observable effect on that of 3-CCA, which is well adsorbed on TiO2 surface.

The photocatalytic activity of TiO2 photocatalysts depends mainly on its crystal phase composition, primary particle size and specific surface area. Shape manipulation is an interesting way to increase the photocatalytic efficiency. The shape-tuning can be carried out at different levels, both at single crystal and polycrystalline agglomeration levels. The aim of our present study was to compare the structural and photocatalytic performances of two type/level of crystal organization of TiO2, namely single crystal shaping vs. polycrystalline/shape tailored agglomeration. The morphological analysis was achieved by XRD, SEM, TEM, Raman spectroscopy, DRS. The photocatalytic performance of the materials was evaluated by the degradation of a model pollutant (phenol). It was found, that both shape manipulating approaches bear the necessary potential which can be exploited in future development of efficient photocatalysts’ synthesis procedures.

The present research focused on the preparation of TiO2/WO3 (76/24 wt. %) composite photocatalysts for the photodegradation of methyl orange under UV light. The composites were prepared by the adjustment of the surface charge of the individual semiconductors, achieving a homogeneous distribution of the components within the composite. This resulted in a homogeneous distribution of the components within the composite. The individual WO3 and TiO2 nanocrystals were obtained either by sol–gel or by hydrothermal synthesis. The produced nanomaterials were characterized by using TEM, SEM, XRD and DRS. Major differences in their photocatalytic performance depended on the nature of the precursors and the synthesis pathway.

For the investigations of the oxidative transformations of various organic substances knowledge of the roles and relative contributions of the reactive species formed to the transformations of the target substances is needed. The vacuum ultraviolet (172 nm) photolysis of aqueous solution of phenol (PhOH) (1.0 × 10−4 mol L−1) as model compound was therefore investigated in this work in the presence or absence of various radical scavenger (tert-butanol, t-BuOH) and transfer materials (dissolved O2; formic acid, HCOOH; sodium formate, HCOONa). It was concluded that the rate of degradation of PhOH increased significantly (up to 3-fold) in the presence of dissolved O2 mainly because of the hindered recombination of the primary radicals (H and OH), the increased concentration of OH. All of the applied organic radical scavenger and radical transfer materials decreased the initial rate of degradation of PhOH mainly by reducing the concentrations of reactive primary radicals. In O2-free solutions, the effects of HCOOH and formate anion (HCOO–) were found to be more significant than that of t-BuOH, which can be explained by the different reactivities of the carbon-centred radicals formed. In O2 saturated solutions, there was no significant difference between the initial rates of transformation determined in the presence of the various additives. In these cases, the less reactive HO2 or O2 – were the most significant species of the radical set, and it seems that these radicals make only minor contributions to the transformation of PhOH, they contribute mainly to the formation of H2O2 instead.

As shape tailoring is gaining more attention in the field of photocatalysis, exploration of the impact of noble metal (Pt) nanoparticles’ morphology on the activity of TiO2–Pt nanocomposites is inevitable. Spherical and polyhedral Pt nanoparticles have been synthesized by chemical reduction, while Aldrich anatase, Aldrich rutile, and Aeroxide P25 were used as base photocatalysts. The nanocomposites were analyzed using DRS, XRD, and HRTEM to uncover morphological, optical, and structural peculiarities of the composite photocatalysts. The importance of the Pt nanoparticles’ geometry was proven at three levels: (i) UV light-driven photodegradation of three model pollutants: phenol, methyl orange, and oxalic acid; (ii) the primary degradation intermediates’ evolution profile in the case of phenol degradation; and (iii) photocatalytic H2 production.

Carbon nanospheres were used as templates for the first time to prepare titania inverse opal photonic crystal. From the spheres, opal colloid crystals were made by vertical deposition on microscope slides, and TiO2 was grown on them using atomic layer deposition (ALD). For this technique, the relatively high thermal stability and the presence of oxygen containing functional groups on the surface of the carbon spheres are beneficial. Subsequent annealing burned out the template spheres, leaving behind the inverse opal structures. The upper solid TiO2 layer was removed with argon ion sputtering. The samples were characterized with SEM, Raman spectroscopy, XRD, EDX, UV–Vis diffuse reflectance spectroscopy and their photocatalytic activity was investigated in decomposing organic dyes under UV and visible illumination. A new approach was used to test photocatalysis on the surface by utilizing UV–Vis reflectance and Raman spectroscopy in conjunction.

This paper presents the preparation of monoclinic WO3 by a one-step hydrothermal method. The effect of very acidic pH (0.1) and the significance of various additives (CH3COOH, NaClO4, Na2SO4) were investigated. To clarify the role of pH on the obtained crystal structure and morphology, every synthesis using pH 1 were repeated, and the effect of temperature, using 180 and 200 °C, was also studied. All samples prepared at pH 0.1 were pure, well crystallized monoclinic WO3 independently from the temperature, the presence and the quality of the additives. At 180 and 200 °C, applying CH3COOH and NaClO4 resulted nanosheets similar in size. With Na2SO4 additive at 180 °C sheets, at 200 °C sheets and also rods formed indicating that SO42− was a capping agent only at 200 °C. For comparison, at pH 1 at both temperatures the crystalline phases and the morphologies varied depending on the type of the additive.

As visible light driven photocatalysis became more and more intensively studied, the first commercial products showed up on the market. Simultaneously controversial results appeared in the literature generating an intensive debate regarding the advantages and draw-backs of nitrogen doping of titania. Hence, the present work focuses on two commercially available and four sol-gel made nitrogen modified titania powders regarding their structure and activity. It is demonstrated that the interstitial nitrogen entities "leak out" from the catalysts if the material is irradiated with UV light, while substitutional nitrogen remains stable. However, the latter one was proven to be less important in the photocatalytic point of view. These observations were also valid in the case of sol-gel made nitrogen modified titanias. Furthermore, the results obtained after applying different spectroscopic methods (IR, XPS and DRS) shown that the yellow color of the titanias, does not necessary mean that a successful doping is achieved. © 2014 Elsevier B.V. All rights reserved.