PIROKLORNE NANOSTRUKTURE NA OSNOVI Bi2O3 IN NJIHOVE KRISTALOGRAFSKE, OPTOELEKTRONSKE IN FOTOKATALITIČNE LASTNOSTI

Bi2O3-based pyrochlore nanomaterials and their photocatalytic, optoelectronic and crystallographic properties are the research topics of this doctoral dissertation. We synthesized these materials at nanoscale, since they are expected to possess photoactivity in the visible-light spectrum, which is an important target for the high-performance photocatalysts. To prepare nanoparticles that are not agglomerated, different synthesis methods (coprecipitation, coprecipitation followed by the digestion, reverse micelle) and post-treatments (furnace or hydrothermal reactor) were examined. Micrometer size materials were prepared with the solid-state reaction and annealing at high temperature. Bi2Ti2O7 nanoparticles were synthesized with the coprecipitation reaction, followed by annealing at 570 °C in the furnace or in the hydrothermal reactor at 230 °C for 18h in NH4OH medium. UV-Vis diffuse reflectance spectra of the Bi2Ti2O7 samples showed that they exhibit the maximum absorption edge at ~420-440 nm. The UV-Vis diffuse reflectance measurements of Bi2Ti2O7 loaded with 10 wt. % of Ag as a co-catalyst showed an enhanced absorbance in the visible region, presumably due to a contribution of Local Surface Plasmon Resonance. The Bi2Ti2O7 nanoparticles are not photocatalytically active under the visible light irradiation without assistance of a sacrificial reagent. The photocatalytic activity does not increase even with Ag as a co-catalyst under visible light irradiation. All samples are active under UV light irradiation, especially the sample with Ag that is able to decolourize 7 mg/L of metyl orange in just 3 min of exposure to UV light. However, H2O2 as a sacrificial reagent increases the photocatalytic activity of Bi2Ti2O7 under visible light irradiation. Phase pure pyrochlore Bi1.647Nb1.118Fe1.157O7 (BNF) nanoparticles were synthesized with coprecipitation reaction and further annealing in the furnace at 570 °C for 7h or 15h and in the hydrothermal reactor at 160 °C for 18h in 3 M or 6 M NaOH medium. The BNF materials exhibit shift toward longer wavelengths in absorbance of visible light (up to ~550-650 nm). This result confirmed that incorporation of Fe in the pyrochlore structure decreases the band gap. The BNF nanoparticles annealed for 7h showed intense photoactivity under visible light irradiation in the presence of a sacrificial reagent. The improved photoactivity, much better than with BNF, was shown for the composite nanoparticles BiOCl/BNF. They decolourize 100 % of the 7 mg/L methyl orange within only 2h of the visible light irradiation in the presence of H2O2. Phase pure pyrochlore Bi1.9Te0.58Fe1.52O6.87 (BTF) nanoparticles were synthesised by coprecipitation reaction and further annealing in the furnace at 570 °C for 7h. Although the BTF nanoparticles include higher amount of Fe than BNF nanoparticles and exhibit narrower band gap, the photoactivity of these nanoparticles is a bit lower than that of BNF nanoparticles. We assume that Fe at some critical concentration causes formation of mid-band states, which act as recombination centers. The same as BiOCl/BNF, the BiOCl/BTF composite is able to decolourize 100 % of the 7 mg/L MO within 2h of the visible light irradiation in the presence of H2O2. Based on the band gap determination and estimation of valence and conduction band levels, the proposed photodecolourization mechanisms are discussed. The conduction band levels of all synthesized materials lie more positively than O2/O2● redox potential (vs. negative hydrogen electrode potential), but are more close to H2O2/●OH redox potential. Thus, we assume that the photogenerated electrons form ●OH radicals, the species that induce dye decolourization under visible light irradiation. We believe that better performance of composite materials (BiOCl/BNF, BiOCl/BTF) is due to the formation of heterojunction, which facilitates the electron transfer between semiconductors, and O2 vacancy states formation in the BiOCl material.V disertaciji so predstavljene fotokatalitske, optoelektronske in kristalografske lastnosti piroklornih nanomaterialov na osnovi Bi2O3. Te materiale smo sintetizirali na nanonivoju, saj se pričakuje, da so nanodelci fotoaktivni v vidnem spektru svetlobe, kar je pomemben cilj za visoko zmogljive fotokatalizatorje. Z namenom priprave neaglomeriranih nanodelcev smo uporabili različne metode sinteze (soobarjanje, soobarjanje z refluksom in metoda reverznih micel) in termične obdelave (peč ali hidrotermalni reaktor). Materiale mikrometerskih velikosti smo pripravili z reakcijo v trdnem in sintranju pri visokih temperaturah. Bi2Ti2O7 nanodelce smo pripravili z reakcijo soobarjanja, čemur je sledilo žganje pri temperaturi 570 °C v peči ali pri temperaturi 230 °C v hidrotermalnem reaktorju v NH4OH mediju. Analiza z UV-Vis difuzivno reflektančno spektrometrijo je pokazala, da imajo vzorci rob maksimalne absorpcije pri ~420-440 nm. Vzorec Bi2Ti2O7 z naloženim Ag (10 ut. %), ki deluje kot ko-katalizator, je pokazal povečano absorpcijo v vidnem delu spektra. Sklepamo, da zaradi lokalizirane površinske plazmonske resonance. Ugotovili smo, da Bi2Ti2O7 nanodelci niso fotoaktivni pod vidno svetlobo brez uporabe H2O2. Tudi ob uporabi Ag kot ko-katalizatorja se fotokatalitska aktivnost delcev ne poveča. Nasprotno so vsi Bi2Ti2O7 vzorci fotoaktivni pod UV svetlobo, posebej vzorec z Ag na površini, ki razbarva metil oranž s koncentracijo 7 mg/L v samo treh minutah. Pod vidno svetlobo je Bi2Ti2O7 material fotoaktiven samo ob dodatku H2O2. Čisto-fazne Bi1.647Nb1.118Fe1.157O7 (BNF) nanodelce smo sintetizirali z reakcijo soobarjanja in žganjem na 570 °C - 7h ali 15h in v hidrotermalnem reaktorju na 160 °C - 18h v 3 M ali 6 M NaOH mediju. Za vse BNF materiale smo opazili rdeči premik absorbance (absorpcijski rob pri ~550-650 nm). Ta rezultat je potrdil vpliv Fe na zmanjšanje prepovedanega pasu. BNF nanodelci, žgani 7h, so pokazali intenzivno fotokatalitsko aktivnost pod vidno svetlobo v prisotnosti H2O2. Še večjo učinkovitost fotoaktivnosti smo dosegli s kompozitnim materialom BiOCl/BNF. Ta material razbarva metil oranž s koncentracijo 7 mg/L v dveh urah osvetljevanja z vidno svetlobo v prisotnosti H2O2. Čisto-fazne Bi1.9Te0.58Fe1.52O6.87 (BTF) nanodelce smo sintetizirali z reakcijo soobarjanja in žganjem na 570 °C - 7h. Čeprav BTF nanodelci vsebujejo večjo koncentracijo Fe kot BNF nanodelci in imajo zato manjši prepovedan pas, je fotoaktivnost teh delcev nižja. Predvidevamo, da Fe povzroči nastanek vmesnih stanj, med valenčnim in prevodnim pasom, ki delujejo kot rekombinacijski centri. Tako kot BiOCl/BNF, tudi BiOCl/BTF kompozit razbarva metil oranž s koncentracijo 7 mg/L v dveh urah osvetljevanja z vidno svetlobo v prisotnosti H2O2. Na podlagi določenega prepovedanega pasu in izračunanih nivojev valenčnih in prevodnih pasov v polprevodnikih smo predlagali mehanizme razbarvanja barvila. Prevodni pasovi sintetiziranih materialov ležijo bolj pozitivno kot nivo O2/O2● redoks potenciala, vendar bliže nivoju H2O2/●OH redoks potenciala. Torej predvidevamo, da foto-generirani elektroni povzročijo nastanek ●OH radikalov, ki so odgovorni za razbarvanje barvila pod vidno svetlobo. Menimo, da sta kompozitna materiala (BiOCl/BNF in BiOCl/BTF) fotokatalitsko učinkovitejša zaradi nastanka p-n spoja, ki pospeši prenos elektronov med polprevodnikoma in nastanka kisikovih vrzeli v BiOCl materialu

Nanoporous stainless steel materials for body implants—review of synthesizing procedures

Despite the inadequate biocompatibility, medical-grade stainless steel materials have been used as body implants for decades. The desired biological response of surfaces to specific applications in the body is a highly challenging task, and usually not all the requirements of a biomaterial can be achieved. In recent years, nanostructured surfaces have shown intriguing results as cell selectivity can be achieved by specific surface nanofeatures. Nanoporous structures can be fabricated by anodic oxidation, which has been widely studied for titanium and its alloys, while no systematic studies are so far available for stainless steel (SS) materials. This paper reviews the current state of the art in the anodisation of SS; correlations between the parameters of anodic oxidation and the surface morphology are drawn. The results reported by various authors are scattered because of a variety of experimental configurations. A linear correlation between the pores’ diameter anodisation voltage was deduced, while no correlation with other processing parameters was found obvious. The analyses of available data indicated a lack of systematic experiments, which are recommended to understand the kinetics of pore formation and develop techniques for optimal biocompatibility of stainless steel

Use of Plasma Technologies for Antibacterial Surface Properties of Metals

Bacterial infections of medical devices present severe problems connected with long-term antibiotic treatment, implant failure, and high hospital costs. Therefore, there are enormous demands for innovative techniques which would improve the surface properties of implantable materials. Plasma technologies present one of the compelling ways to improve metal’s antibacterial activity; plasma treatment can significantly alter metal surfaces’ physicochemical properties, such as surface chemistry, roughness, wettability, surface charge, and crystallinity, which all play an important role in the biological response of medical materials. Herein, the most common plasma treatment techniques like plasma spraying, plasma immersion ion implantation, plasma vapor deposition, and plasma electrolytic oxidation as well as novel approaches based on gaseous plasma treatment of surfaces are gathered and presented. The latest results of different surface modification approaches and their influence on metals’ antibacterial surface properties are presented and critically discussed. The mechanisms involved in bactericidal effects of plasma-treated surfaces are discussed and novel results of surface modification of metal materials by highly reactive oxygen plasma are presented

Crystallized TiO2_2 nanosurfaces in biomedical applications

Crystallization alters the characteristics of TiO$_2$ nanosurfaces, which consequently influences their bio-performance. In various biomedical applications, the anatase or rutile crystal phase is preferred over amorphous TiO$_2$. The most common crystallization technique is annealing in a conventional furnace. Methods such as hydrothermal or room temperature crystallization, as well as plasma electrolytic oxidation (PEO) and other plasma-induced crystallization techniques, present more feasible and rapid alternatives for crystal phase initiation or transition between anatase and rutile phases. With oxygen plasma treatment, it is possible to achieve an anatase or rutile crystal phase in a few seconds, depending on the plasma conditions. This review article aims to address different crystallization techniques on nanostructured TiO$_2$ surfaces and the influence of crystal phase on biological response. The emphasis is given to electrochemically anodized nanotube arrays and their interaction with the biological environment. A short overview of the most commonly employed medical devices made of titanium and its alloys is presented and discussed

Dental silicate ceramics surface modification by nonthermal plasma

Objectives: Nonthermal atmospheric or low-pressure plasma (NTP) can improve the surface characteristics of dental materials without affecting their bulk properties. This study aimed to systematically review the available scientific evidence on the effectiveness of using NTP for the surface treatment of etchable, silica-based dental ceramics before cementation, and elucidate its potential to replace the hazardous and technically demanding protocol of hydrofluoric acid (HF) etching. Methods: A valid search query was developed with the help of PubMed\u27s Medical Subject Headings (MeSH) vocabulary thesaurus and translated to three electronic databases: PubMed, Web of Science, and Scopus. The methodological quality of the studies was assessed according to an adapted version of the Methodological Index for Non-Randomized Studies (MINORS). Results: Thirteen in vitro study reports published between 2008 and 2023 were selected for the qualitative and quantitative data synthesis. The implemented methodologies were diverse, comprising 19 different plasma treatment protocols with various device settings. Argon, helium, oxygen, or atmospheric air plasma may significantly increase the wettability and roughness of silicate ceramics by plasma cleaning, etching, and activation, but the treatment generally results in inferior bond strength values after cementation compared to those achieved with HF etching. The technically demanding protocol of plasma-enhanced chemical vapor deposition was employed more commonly, in which the surface deposition of hexamethyl disiloxane with subsequent oxygen plasma activation proved the most promising, yielding bond strengths comparable to those of the positive control. Lack of power analysis, missing adequate control, absence of examiner blinding, and non-performance of specimen aging were common methodological frailties that contributed most to the increase in bias risk (mean MINORS score 15.3 ± 1.1). Significance: NTP can potentially improve the adhesive surface characteristics of dental silicate ceramics in laboratory conditions, but the conventional protocol of HF etching still performs better in terms of the resin-ceramic bond strength and longevity. More preclinical research is needed to determine the optimal NTP treatment settings and assess the aging of plasma-treated ceramic surfaces in atmospheric conditions

Nanoporous stainless steel materials for body implants—review of synthesizing procedures

Despite the inadequate biocompatibility, medical-grade stainless steel materials have been used as body implants for decades. The desired biological response of surfaces to specific applications in the body is a highly challenging task, and usually not all the requirements of a biomaterial can be achieved. In recent years, nanostructured surfaces have shown intriguing results as cell selectivity can be achieved by specific surface nanofeatures. Nanoporous structures can be fabricated by anodic oxidation, which has been widely studied for titanium and its alloys, while no systematic studies are so far available for stainless steel (SS) materials. This paper reviews the current state of the art in the anodisation of SScorrelations between the parameters of anodic oxidation and the surface morphology are drawn. The results reported by various authors are scattered because of a variety of experimental configurations. A linear correlation between the pores’ diameter anodisation voltage was deduced, while no correlation with other processing parameters was found obvious. The analyses of available data indicated a lack of systematic experiments, which are recommended to understand the kinetics of pore formation and develop techniques for optimal biocompatibility of stainless steel