Optimization of the preparation and structural properties of doped nanosized titanium dioxide

V zadnjih desetletjih postaja dostop do čiste vode vse večja težava, ki jo lahko pripišemo eksponentni rasti prebivalstva in industrializaciji, zaradi česar se je pojavila potreba po ponovni uporabi očiščenih vod. V ta namen je bilo razvitih veliko metod za čiščenje odpadnih voda, ki pa so lahko pri odstranjevanju težje odstranljivih organskih onesnažil manj učinkovite ali celo neučinkovite. Enega največjih problemov predstavljajo odpadne vode v tekstilni industriji, saj so se konvencionalne metode čiščenja izkazale kot zelo neučinkovite pri odstranjevanju tekstilnih barvil, zaradi česar odpadne vode ostanejo obarvane. To lahko vodi do sprememb v bioloških ciklih vodnih organizmov, saj obarvanost preprečuje dostop sončne svetlobe in s tem zmožnost poteka fotosinteze v takem deležu, kot le-ta poteka v prosojni vodi. Zaradi tega se je pojavila potreba po razvoju tehnologije, ki bi lahko učinkovito odstranila onesnažila, prisotna v odpadnih vodah. Fotokataliza se je zaradi svoje zmožnosti popolne mineralizacije organskih onesnažil (razgradnja do CO2 in H2O) na tem področju izkazala za zelo obetavno metodo. Proces fotokatalize temelji na osvetljevanju fotokatalizatorja s svetlobo določene valovne dolžine, ki vzbudi elektrone iz valenčnega v prevodni pas, pri čemer v valenčnem pasu nastanejo elektronske vrzeli. Generirani nosilci naboja nato potujejo do površine fotokatalizatorja, kjer preko nastalih močno reaktivnih specij reagirajo z adsorbiranim onesnažilom in posledično katalizirajo njegovo razgradnjo. Pri fotokatalizi se kot fotokatalizator najpogosteje uporablja TiO2. Zaradi širine njegovega prepovedanega pasu med (3,2 eV za anatas) lahko fotokatalitske reakcije potekajo predvsem pri osvetljevanju s svetlobo z valovno dolžino, nižjo od 390 nm (UV območje). Zaradi tega je bilo v zadnjih desetletjih veliko raziskav posvečenih zoževanju prepovedanega pasu TiO2, s čimer bi se povečala njegova fotokatalitska aktivnost pri osvetljevanju z vidno svetlobo. V dokrorskem delu delu sem se ukvarjal s sintezo TiO2, ki bi imel čim višjo fotokatalitsko aktivnost pri osvetljevanju z vidno svetlobo, kar sem dosegel z dopiranjem z nekovinami in kovinami. Vzorci TiO2 so bili pripravljeni s sol-gel sintezo, z uporabo TiCl4 kot prekurzorja (anorganska pot). Stabilnost solov sem dosegel z ustrezno nizko vrednostjo pH, kar sem dosegel z nakisanjem z uporabo različnih kislin (HCl in H2SO4). V vzorce sem dodal še različne dopante, ki so delovali kot vir dopiranega dušika (sečnina, NH4NO3), žvepla (tiosečnina) in platine (H2PtCl6). Pripravljene raztopine sola sem nato z uporabo tehnike potapljanja (dip-coating) nanesel na objektna stekelca in silicijeve rezine, kristalizacijo amorfnega TiO2 pa sem dosegel s termično obdelavo v komorni peči. Prahove sem pripravil s sušenjem raztopine sola do kserogela in nadaljnjo termično obdelavo v komorni peči. Fotokatalitska učinkovitost tankih plasti pri osvetljevanju z UV in vidno svetlobo sem določil z meritvami hitrosti razgradnje organskega barvila Plasmocorinth B, ki se veliko uporablja v tekstilni industriji. Fotokatalitsko aktivnost prahov je bila določena z merjenjem hitrosti oksidacije izopropanola v aceton. Strukturne in morfološke lastnosti tankih plasti in ustreznih prahov so bile določene z uporabo različnih karakterizacijskih metod. Prav tako sem z uporabo različnih tehnik (kromatografija, meritve pH in prevodnosti) določil mehanizem razgradnje Plasmocorinth B. Ugotovil sem, da so strukturne in morfološke lastnosti tankih plasti in prahov odvisne od vrste in količine dodane kisline, dopanta in temperature termične obdelave. Vsi omenjeni parametri imajo velik vpliv na fotokatalitsko aktivnost tankih plasti in prahov. Vzorci, dopirani in ko-dopirani s kovinami in nekovinami imajo veliko višjo aktivnost pri osvetljevanju z UV in vidno svetlobo. Najbolj aktivni so bili vzorci, kodopirani z dušikom in žveplom, modificirani s platino.Access to clean water has become a major problem in the last decades. This is due to the exponential growth of human population and industrialization. Because of this, the need for reuse of treated waste waters has arisen. A lot of methods for waste water treatment have been developed, but they can be inefficient for the degradation of persistent organic pollutants. A major environmental problem are textile industry effluents since conventional treatment methods are not able to remove textile dyes from waste waters. Because of that, waste waters remain colored, which can alter biological cycles of water organisms, by blocking access of sunlight and consequentially blocking photosynthesis. There is therefore a need for the development of a method, which could efficiently degrade pollutants present in textile industry waste waters. Because of its ability to completely oxidize organic pollutants to CO2 and H2O, photocatalysis has emerged as a promising technique for waste water treatment. The term photocatalysis is used to describe a process during which light of a certain wavelength excites an electron from the valence band onto the conductive band of a photocatalyst. The resulting charge carriers (electron and hole) then travel to the surface of the photocatalyst, where they can catalyze the degradation of adsorbed organic pollutants. Because of its advantageous properties, titanium dioxide (TiO2) has been one of the most widely used photocatalysts. One of the main drawbacks of TiO2 is the width of its band gap (3.2 eV for anatase), which means that an electron can only be excited onto the conduction band when illuminated with UV light with a wavelength lower than 390 nm. A lot of studies have focused on narrowing the width of the band gap of TiO2, which would increase its photocatalytic activity under visible light illumination. In my research work, I focused on preparing TiO2 with high photocatalytic activity under visible light illumination. This was achieved by non-metal and metal doping. Samples were synthesized using a sol-gel synthesis with titanium tetrachloride as a precursor (inorganic path). During the synthesis, solutions were acidified with two different acids (HCl and H2SO4). To increase the activity of TiO2 under visible light illumination, diferent dopants, acting as a source of doped nitrogen (NH4NO3, urea), sulfur (thiourea) and platinum (H2PtCl6), were added. Afterward, the prepared sols were deposited onto object glasses using dip-coating and thermally treated in a muffle furnace to promote crystallization. Corresponding powders were prepared by drying the prepared sols, followed by thermal treatement in a muffle furnace. Photocatalytic activity of the prepared thin films was tested by observing the degradation rate of Plasmocorinth B textile dye. The photocatalytic activity of powders was determined by observing the rate of isopropanol to acetone oxidation. Thin films and corresponding powders were characterized by various techniques. Moreover, the degradation mechanism of Plasmocorinth B was determined using various techniques (chromatography, pH and conductivity). Results of these characterization techniques have shown that the type and amount of acid and dopant used and also the temperature of thermal treatment have a large effect on the structural, surface and morphological properties and consequentially the photocatalytic activity of thin films and corresponding powders. Results have shown a significant increase in activity in samples, doped and co-doped with metals and non-metals, under UV and visible light illumination. The highest activity was observed in samples, co-doped with nitrogen and sulfur and modified with platinum

One-Pot Synthesis of Sulfur-Doped TiO2/Reduced Graphene Oxide Composite (S-TiO2/rGO) with Improved Photocatalytic Activity for the Removal of Diclofenac from Water

Sulfur-doped TiO2 (S-TiO2) composites with reduced graphene oxide (rGO), wt. % of rGO equal to 0.5%, 2.75%, and 5.0%, were prepared by a one-pot solvothermal procedure. The aim was to improve photocatalytic performance in comparison to TiO2 under simulated solar irradiation for the treatment of diclofenac (DCF) in aqueous medium. The obtained composites were characterized for physical- chemical properties using thermogravimetric analysis (TGA), X-ray diffractograms (XRD), Raman, scanning electron microscopy (SEM)/energy dispersive X-ray (EDX), Brauner Emmett Teller (BET), and photoluminescence (PL) analyses, indicating successful sulfur doping and inclusion of rGO. Sulfur doping and rGO have successfully led to a decrease in photogenerated charge recombination. However, both antagonistic and synergistic effects toward DCF treatment were observed, with the latter being brought forward by higher wt.% rGO. The composite with 5.0 wt.% rGO has shown the highest DCF conversion at pH 4 compared to that obtained by pristine TiO2, despite lower DCF adsorption during the initial dark period. The expected positive effects of both sulfur doping and rGO on charge recombination were found to be limited because of the subpar interphase contact with the composite and incomplete reduction of the GO precursor. Consequent unfavorable interactions between rGO and DCF negatively influenced the activity of the studied S-TiO2/rGO photocatalyst under simulated solar irradiation

Green Synthesis of Immobilized CuO Photocatalyst for Disinfection of Water

A green method for depositing a CuO layer with good adhesion and a large surface area on a support of activated alumina (Al2O3) was evaluated. The relatively simple method consists of adsorption of a copper salt on the surface of Al2O3, formation of Cu(OH)2, and subsequent decomposition of the hydroxide to CuO. The XRD confirmed that the deposited photocatalyst crystalized at low temperatures (80 °C). Furthermore, BET measurements show a surface area of about 90 m2/g. The large surface area is the result of the speed of the conversion and decomposition reactions. The photokilling properties of the prepared photocatalyst were evaluated using E. coli cells and the leaching of copper ions was determined using ICP-MS. The photocatalytic efficiency was also evaluated by the degradation of an organic azo dye. The prepared photocatalyst shows good activity in the purification and disinfection of treated water. The described method is economical, fast, and can be considered green, since the only byproducts are water and NaCl

Synthesis of nanostructured TiO2_2 microparticles with high surface area

Hydrothermal reactions represent a simple and efficient method for the preparation of nanostructured TiO$_2$ particles that could be of interest as photocatalysts or catalytic supports. Although the particle size is in the range of 2–5 µm, the nanostructures composing the particles ensure a large specific surface area with values above 100 m$^2$/g. The effects of the different synthesis parameters on the morphology, photocatalytic activity, and stability of the prepared material were studied. The surface morphology of the prepared TiO$_2$ powders was studied by scanning electron microscopy (SEM). To further characterize the samples, the specific surface area for different morphologies was measured and the photocatalytic activity of the prepared powders was tested by degrading model pollutants under UV irradiation. The results show that the initial morphology had little effect on the photocatalytic properties. On the other hand, the final calcination temperature significantly increased the degradation rates, making it comparable to that of P25 TiO$_2$ (particle size 20–30 nm)

Metal and non-metal modified titania: the effect of phase composition and surface area on photocatalytic activity

The application of TiO2 photocatalysis in various environmental fields has been extensively studied in the last decades due to its ability to induce the degradation of adsorbed organic pollutants. In the present work, TiO powders doped and co-doped with sulfur and nitrogen and modified with platinum were prepared by particulate sol-gel synthesis. PXRD measurements revealed that the replacement of HCl with H2SO4 during synthesis reduced the size of the crystallites from similar to 30 nm to similar to 20 nm, increasing the surface area from similar to 44 m(2)/g to similar to 80 m(2)/g. This is consistent with the photocatalytic activity of the samples and the measured photocurrent behavior of the photocatalysts. The results showed that the properties of the powders (i.e., surface area, crystallite size, photocurrent behavior) depend strongly not only on the type but also on the amount of acid and dopants used in the synthesis. Doping, co-doping and modification of TiO2 samples with nitrogen, sulfur and platinum increased their photocatalytic activity up to 6 times.Web of Science69122621

Increasing the photocatalytic efficiency of ZnWO4_4 by synthesizing a Bi2_2WO6_6/ZnWO4_4 composite photocatalyst

In the present study, a Bi$_2$WO$_6$/ZnWO$_4$ photocatalyst was successfully constructed by a modified hydrothermal synthesis method with different molar concentrations of Bi$_2$WO$_6$ with respect to ZnWO$_4$. The variation in molar concentrations of Bi$_2$WO$_6$ changed the photocatalytic properties of the Bi$_2$WO$_6$/ZnWO$_4$ catalyst. The synthesized Bi$_2$WO$_6$/ZnWO$_4$ photocatalyst was characterized by various techniques to decipher its structural and spectral properties. The interaction of Bi$^{2+}$ ionic charge carriers and many-body effects cause the band gap to narrow in Bi$_2$WO$_6$/ZnWO$_4$, as shown by PL analysis. The decrease in band gap energies (E$_g$) from 4.7 eV (ZnWO$_4$) to 3.5 eV (30% Bi$_2$WO$_6$/ZnWO$_4$) is beneficial because less energy is required to excite the valence electrons. The maximum degradation of Plasmocorinth B dye was found with 30% Bi$_2$WO$_6$/ZnWO$_4$ under UV irradiation. This increased activity of 30% Bi$_2$WO$_6$/ZnWO$_4$ can be attributed to the (i) synergistic effect in the bicrystalline framework of Bi$_2$WO$_6$ and ZnWO$_4$, (ii) the high close contact between Bi$_2$WO$_6$ and ZnWO$_4$, and (iii) the small crystallite size. The photocatalytic activity of synthesized Bi$_2$WO$_6$/ZnWO$_4$ photocatalyst shows its significant potential in water/ wastewater treatment application

Removal of 18 bisphenols co-present in aqueous media by effectively immobilized titania photocatalyst

In recent years, the increasing demand for clean and potable water has created a need for efficient, cost-effective wastewater treatment. One of the most promising methods is heterogeneous photocatalysis due to its ability to mineralize organic molecules. This paper describes the development of a flow-through packed bed reactor system based on a packed column comprising glass beads coated with commercially available TiO$_2$ (P25). The resulting deposited films and corresponding powders were characterized using thermal analysis (TGA–DSC–MS), X-ray diffraction (XRD), scanning/transmission electron microscopy (SEM/TEM), specific surface area (BET) and X-ray photoelectron spectroscopy (XPS) measurements. The photocatalytic efficiency of the reactor was tested by observing the degradation rate of Plasmocorinth B, an organic dye, and 18 bisphenols co-dissolved in deionized water and simulated wastewater under UV light. The developed photocatalytic reactor effectively removed organic dye and bisphenols from the aqueous medium using a combination of adsorption and photocatalysis

Effective production of formic and acetic acid via CO2 hydrogenation with hydrazine by using ZrO2 catalysts

Amorphous ZrO2 and Mn addition to ZrO2 catalysts were studied for CO2 hydrogenation to formic acid and acetic acid via an indirect hydrogen source, i.e., hydrazine monohydrate. The amorphous ZrO2 was synthesized by the precipitation method and the Mn addition was carried out by two different methods, namely, the physical mixing method (Mn+ZrO2) and the co-precipitation method (Mn-ZrO2). The XRD and XPS results show that the enhanced metal-support interaction in the co-precipitation method leads to the stabilization of Mn in its higher oxidation state. The physical mixing method leads to the stabilization of Mn in its lower oxidation state and/or metallic form, which improves hydrogen production from hydrazine and thus CO2 hydrogenation. Optimization of reaction parameters was investigated with changes in reaction conditions such as reaction time, CO2 pressure and catalyst weight.Web of Science545art. no. 11323

Enhancing the Photocatalytic Performance of BiVO₄ for Micropollutant Degradation by Fe and Ag Photomodification

Wider application of BiVO4 (BVO) for photocatalytic water treatment is primarily limited by its modest photocatalytic effectiveness, despite its appropriately narrow band gap for low-cost, sunlight-facilitated water treatment processes. In this study, we have photomodified an isotype BVO, consisting of a tetragonal zircon and monoclinic scheelite phase, with Fe (Fe@BVO) and Ag (Ag@BVO) ionic precursors under UV illumination in an aqueous ethanol solution in order to assess their effect on the opto-electronic properties and effectiveness for the removal of ciprofloxacin (CIP). Fe@BVO failed to demonstrate enhanced effectiveness over pristine BVO, whereas all Ag@BVO achieved improved CIP degradation, especially 1% Ag@BVO. At pH 4 and 6, 1% Ag@BVO demonstrated nearly 24% greater removal of CIP than BVO alone. Photomodification with Fe created surface oxygen vacancies, as confirmed by XPS and Mott–Schottky analysis, which facilitated improved electron mobility, although no distinct Fe-containing phase nor Fe-doping was detected. On the other hand, the introduction of mid-band gap states by oxygen vacancies decreased the reducing power of the photogenerated electrons as the flat band potentials were shifted to more positive values, thus likely negatively impacting superoxide formation. In contrast, Ag-photomodification (Ag@BVO) resulted in the formation of Ag2O/AgO and Ag nanoparticles on the surface of BVO, which, under illumination, generated hot electrons by surface plasmon resonance and enhanced the mobility of photogenerated electrons. Our research underscores the pivotal role of photogenerated electrons for CIP degradation by BiVO4-based materials and emphasizes the importance of appropriate band-edge engineering for optimizing contaminant degradation

Photocatalytic sol-gel/P25 TiO2_2 coatings for water treatment

The effect of different water matrices on the photocatalytic degradation of dissolved pharmaceuticals was explored. The focus was on the degradation efficiencies in wastewater effluent from a bioreactor and water effluent from a central wastewater treatment plant and comparing the results with degradation in deionized H$_2O$. The compounds tested included: oxytetracycline, marbofloxacin, ibuprofen, diclofenac, phenytoin, ciprofloxacin, sulfamethoxazole. For the experiments performed in this study, a compact packed-bed photocatalytic reactor was used in which the hybrid TiO$_2$ photocatalyst (sol-gel/P25) was deposited on ∼3 mm glass beads. As expected, the reactions proceed more slowly in wastewater than in deionized water, yet it is shown that removal of the compounds from the water is still possible even when other organic molecules are present. Total organic carbon measurements have shown that complete mineralization takes place albeit at slower rates than the initial degradation of parent compounds. The results show that an acidic pH can increase the reaction rates and the adsorption on the photocatalyst surface. Analyses of the degradation intermediates were performed using tandem liquid chromatography triple-quadrupole mass spectrometry system. Additionally, X-ray absorption spectroscopy was applied to get insight into the local structure of the photocatalyst before and after use. Understanding the effects that different wastewater compositions have on photocatalytic reactions will help to refine the potential applications of the technology