Synthesis of mesoporous Mn/TiO2 nanocomposites and investigating the photocatalytic properties in aqueous systems

Visible light photocatalytic degradation of methylene blue and rhodamine B over silver-doped titanium dioxide nanocomposites supported on Fuller's earth

Silver-doped-titanium dioxide nanoparticles supported on Fuller's earth, prepared by the sol-gel method, were characterized with XRD, TGA, zeta potential, SEM, EDX, TEM, XPS, photoluminescence and UV-DRS measurements. The material, Ag-TiO2-Fuller's earth (AgTF), was tested for photocatalytic activity concerning the degradation of rhodamine B (RhB) and methylene blue (MB) in aqueous solution under visible light irradiation with pH, catalyst dosage, and dye concentration as the process variables. The degradation kinetics indicated pseudo-first-order kinetics with rate constant of (i) 0.55 min-1with 0.12 gL-1AgTF loading, 10-5 M MB at pH 9, and (ii) 0.53 min-1 with 0.08 g L-1 AgTF loading, 5 × 10-5 M RhB at pH 8. The methylene blue degradation was maximum (98.66%) for AgTF loading of 0.12 g L-1 while the maximum RhB degradation (96.34%) was attained with AgTF loading of 0.08 g L-1. With 5 × 10-6M MB concentration, the degradation achieved was 98% in 45 min and 100% in 60 min. One hundred per cent degradation of the dye, RhB (1 × 10-6 M) could be achieved in 30 min with 0.08 g L-1 AgTF at pH 8. The use of Fuller's earth, a cheap, abundant and large surface area support, increases the adsorbability of the dye on the catalyst surface and hence promotes the degradation. The catalyst could be removed easily from the reaction mixture and reused for up to five cycles without any significant decrease in activity. Scavengers such as triethanolamine (TEOA), p-benzoquinone (BQ) and isopropyl alcohol (IPA) were utilized to get some insight into the photocatalysis mechanism.

Photocatalytic H2 production and degradation of aqueous 2-chlorophenol over B/N-graphene-coated Cu0/TiO2: A DFT, experimental and mechanistic investigation

Energy and environmental challenges are global concerns that scientists are interested in alleviating. It is on this premise that we prepared boron/nitrogen graphene-coated Cu0/TiO2 (B/N-graphene-coated Cu/TiO2) photocatalyst of varying B:N ratios with dual functionality of H2 production and 2-Chlorophenol (2-CP) degradation. In-situ coating of Cu0 with B/N-graphene is achieved via solvothermal synthesis and calcination under an inert atmosphere. All B/N-graphene-coated Cu/TiO2 exhibit higher photonic efficiencies (5.68%-7.06% at 300 < λ < 400 nm) towards H2 production than bare TiO2 (0.25% at 300 < λ < 400 nm). Varying the B:N ratio in graphene influences the efficiency of H2 generation. A B:N ratio of 0.08 yields the most active composite exhibiting a photonic efficiency of 7.06% towards H2 evolution and a degradation rate of 4.07 × 10-2 min-1 towards 2-chlorophenol (2-CP). Density functional theory (DFT) investigations determine that B-doping (p-type) enhances graphene stability on Cu0 while N-doping (n-type) increases the reduction potential of Cu0 relative to H+ reduction potential. X-ray photoelectron spectroscopy reveals that increasing the B:N ratio increases p-type BC2O while decreasing n-type pyridinic-N in graphene thus altering the interlayer electron density. Isotopic labelling experiments determine water reduction as the main mechanism by which H2 is produced over B/N-graphene-coated Cu/TiO2. The reactive species involved in the degradation of 2-CP are holes (h+), hydroxyl radical (OH•), and O2•-, of which superoxide (O2•-) plays the major role. This work displays B/N -graphene-coated Cu/TiO2 as a potential photocatalyst for large-scale H2 production and 2-CP degradation.

High efficiency photocatalytic degradation of Ambroxol over Mn doped TiO2: Experimental designs, identification of transformation products, mineralization and mechanism

Ambroxol (AMB) is a drug commonly used for chronic bronchitis prevention. Once released in surface water, this recalcitrant chemical becomes a hazardous pollutant. Here, we investigated the ability of 1% Mn-doped TiO₂ (Mn-TiO₂) to mineralize AMB by photocatalysis. We studied the morphology, and the physical and electrochemical properties of Mn-TiO₂ using X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy, X-ray fluorescence, BET method, UV-visible, and electrochemical study and optimized the AMB degrading experimental conditions through response surface methodology (RSM). Mn-TiO₂ at the dose of 0.625 g·L^-1 allowed the complete photodegradation of AMB (30 ppm) at pH 7 under UVA light irradiation for 30 min while total mineralization in CO₂ (>96%) was achieved after 24 h of irradiation. Mn-TiO₂ was 1.6-time more efficient than TiO₂ Degussa P25. Product studies were also carried out by liquid chromatography coupled to electrospray high resolution mass spectrometry. Twenty-one photodegradation products were detected and identified. In addition, ionic chromatography analyses revealed the release of Br^-, NH₄⁺, and NO₃^- at respectively 97, 63 and 35% of the total Br, and N initially present in AMB. Finally, the reusability of the photocatalyst was also tested. After four cycles, the almost complete photodegradation of AMB was achieved showing that Mn-TiO₂ was highly stable. This work brings new physical characteristics on Mn-TiO₂ photocatalyst. Moreover, it is the first study investigating the photocatalytic degradation of recalcitrant AMB drug.

Machine Learning Band Gaps of Doped-TiO2 Photocatalysts from Structural and Morphological Parameters

Titanium dioxide (TiO₂) photocatalysts in the form of thin films are of great interest due to their tunable optical band gaps, E _g's, which are promising candidates for applications of visible-light photocatalytic activities. Previous studies have shown that processing conditions, dopant types and concentrations, and different combinations of the two have great impacts on structural, microscopic, and optical properties of TiO₂ thin films. The lattice parameters and surface area are strongly correlated with E _g values, which are conventionally simulated and studied through first-principle models, but these models require significant computational resources, particularly in complex situations involving codoping and various surface areas. In this study, we develop the Gaussian process regression model for predictions of anatase TiO₂ photocatalysts' energy band gaps based on the lattice parameters and surface area. We explore 60 doped-TiO₂ anatase photocatalysts with E _g's between 2.280 and 3.250 eV. Our model demonstrates a high correlation coefficient of 99.99% between predicted E _g's and their experimental values and high prediction accuracy as reflected through the prediction root-mean-square error and mean absolute error being 0.0012 and 0.0010% of the average experimental E _g, respectively. This modeling method is simple and straightforward and does not require a lot of parameters, which are advantages for applications and computations.

Porous nickel doped titanium dioxide nanoparticles with improved visible light photocatalytic activity

A green hydrothermal synthesis route to prepare a porous nickel doped titanium dioxide (Ni-TiO₂) nanostructured photocatalyst has been developed in this research. The results show that Ni doping can greatly increase the visible light photocatalytic performance of TiO₂ through the introduction of impurity bands in the band gap of TiO₂. After 5 cycles of reuse, Ni-TiO₂ nanoparticles still show stable photocatalytic activity for MB degradation. The Ni-TiO₂ nanoparticles developed in the present study are expected to have great potential applications in wastewater treatment due to the advantages of strong visible light photocatalytic performance, a simple synthetic process and high cycle utilization performance.

Synthesis of lanthanide-doped TiO2 nanoparticles and their photocatalytic activity under visible light

Four different lanthanide (Ce, Dy, Lu, and Sm) doped TiO2 mesoporous materials were synthesised using the sol–gel method with titanium (IV) isopropoxide as the precursor. All of the synthesized materials were characterised using different analytical techniques, BET, PXRD, TEM, SEM-EDX, Raman, FTIR, photoluminescence, and UV-DRS spectroscopy. Photocatalytic activity and efficacy of the materials in the degradation of caffeine in aqueous solutions was investigated under visible light illumination. Although all materials showed good photocatalytic activity, Ce-doped TiO2 exhibited relatively better activity than the other three catalysts. High photoactivity of the catalysts was attributed to the presence of lanthanides and their ability to generate ions that scavenge electrons under visible light, thereby enhancing photodegradation of caffeine. All materials proved to be good and were recyclable without loss of catalytic activity up to three runs. An intermediate [N-1,3,6-trimethyl-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-5-yl)formamide] (TDTF) and two products (6-amino-1,3-dimethyl-2,4-dioxo-1,2,3,4-tetrahydropymidin-5-ly)-(methyl)-carbamic acid (ATCA) and N-methyl-N-(methylcarbomoyl)-2-oxoacetamide (MMO) were identified by the LC–MS spectra.

Electrochemical anodization of graphite oxide-TiO2 nanotube composite for enhanced visible light photocatalytic activity

The electrochemical anodization method was used to dope graphite oxide (GO) onto TiO₂ nanotubes (TNTs). This study focused on enhancement of the photocatalytic activity of TNTs in the visible light region. In this study, we have checked the effect of different GO concentrations and effect of GO doping time on photocatalytic efficiency of composite. The photocatalytic activity of the GO-TNT composite was tested by degradation of an organic compound. The organic compound was most severely degraded (95%) when the GO-TNT catalyst was doped at an anodization of 60 V for 13 min and GO concentration of 0.25 g L^-1. This degradation was 5.6 times higher than that of bare TiO₂. The as-prepared catalyst was characterized using FE-SEM, XRD, AES, PL, UV-Vis DRS, and Raman analysis. Recycling of the GO-TNT composite was also performed in order to examine the stability of the visible light catalyst. We observed that the doping of GO on the TNT surface can enhance the photocatalytic efficiency under visible light. Graphene acts as an electron transport; therefore, GO-TNTs were favorable for the separation of e^- and h⁺ charges. This promoted the formation of OH radicals, h⁺, and superoxides, all of which degrade organics.

Photocatalytic oxidation of nitrogen oxides over {001}TiO2: the influence of F- ions

A series of anatase TiO₂ nanosheets with different percentage of {001} facets ({001}TiO₂) were synthesized through a hydrothermal route using tetrabutyltitanate as a titanium precursor and HF as a shape controlling agent. The amount of HF exhibits an obvious influence on the structures and activities of TiO₂ samples. The adsorbed surface F^- ions on the {001} facets of the anatase TiO₂ were removed by washing them with NaOH solution. The as-prepared catalysts were characterized by X-ray diffraction, Brunner-Emmet-Teller measurements, ultraviolet-visible diffuse reflectance spectroscopy, scanning electron microscopy, transmission electron microscopy techniques, and X-ray photoelectron spectroscopy analysis. The results indicated that all the as-prepared catalysts showed an anatase crystalline and nanosheet structure, as well as a strong ultraviolet light absorbance. With the increase of HF content, the crystallite size and the percentage of {001} facets increased first and later decreased, state the opposite change observed in BET. When the content of HF was 4.4 mL, the percentage of {001} facets reached the maximum up to 61.62%. After all samples were treated with 0.1 M NaOH solution, the percentage of {001} facets increased to a maximum of 64.46%. All the samples washed by NaOH solution exhibited much higher photocatalytic activity for NO_x oxidation under UV light irradiation than P25, {101}TiO₂, and {001}TiO₂ without NaOH washing, suggesting that the surface F^- ions inhibited the photocatalytic NO_x oxidation. Moreover, the results showed that the NaOH-washed {001}TiO₂ has a high humidity tolerance.

Enhancement of visible-light photocatalytic activities of BiVO4 coupled with g-C3N4 prepared using different precursors

Graphitic-like carbon nitride (g-C₃N₄) photocatalyst was synthesized by a facile chemical pyrolysis method, which was built on the self-condensation of different precursors to generate g-C₃N₄, e.g., melamine, urea, and thiocarbamide. And the different precursors produced a great influence on the photocatalytic activities of g-C₃N₄. Heterojunctions of g-C₃N₄ and BiVO₄ were synthesized using a facile solvent evaporation method. The formation of BiVO₄/g-C₃N₄ composites were confirmed by XRD, FT-IR, SEM, XPS, and UV-Vis DRS. The photocatalytic activities for RhB degradation were evaluated under visible-light irradiation. The photocatalytic activity of g-C₃N₄ prepared by urea was higher than that of g-C₃N₄ prepared by melamine and thiocarbamide, which was attributed to its favorable dispersibility, larger specific surface area, and higher oxidation capacity. The heterojunction composites exhibited higher photocatalytic activity than pure g-C₃N₄ or BiVO₄. The results showed obvious removal efficiency for RhB, and the optimal sample with a BiVO₄ content of 10% exhibited higher efficiency than pure g-C₃N₄ and BiVO₄, and 10 wt%BiVO₄/CN-U showed the highest photocatalytic activity. The enhanced photocatalytic activity of BiVO₄/g-C₃N₄ composite can be attributed to the intimate coupling between the two host substrates, resulting in an efficient charge separation.

Facile microwave synthesis of pine cone derived C-doped TiO2 for the photodegradation of tetracycline hydrochloride under visible-LED light

Pine cone derived carbon was doped into TiO₂ via a facile microwave procedure at different powers, different from other conventional synthesis methods. The materials were adequately characterized and applied in the photodegradation of 5 mg/L tetracycline hydrochloride (TA) under visible-LED light. The XRD results showed that all materials exist as both anatase and rutile phase. However, both the microwave power and the carbon content of the composite material inhibited the conversion of anatase into rutile. The composite material synthesized at a microwave power of 800 W (CT800), displayed the highest band gap energy (3.14 eV) but showed the least electron-hole recombination rate. Hence, CT800 exhibited the highest apparent rate constant of 9.9 × 10^-3 min^-1 and a half-life of 70 min. An inverse relationship between OH^• radical scavenger (isopropanol) and the percentage degradation by CT800 suggests that OH^• is majorly responsible for the degradation of TA. Recyclability studies revealed that after 4 cycles of photocatalytic degradation reactions, CT800 retained approximately 83% performance confirming its stability and reusability.

Nano-MnO₂ Decoration of TiO₂ Microparticles to Promote Gaseous Ethanol Visible Photoremoval

TiO₂-based photocatalysis under visible light is an attractive way to abate air pollutants. Moreover, developing photocatalytic materials on a large-scale requires safe and low-cost precursors. Both high-performance TiO₂ nanopowders and visible-light active noble metals do not match these requirements. Here, we report the design of novel Mn-decorated micrometric TiO₂ particles. Pigmentary TiO₂ replaced unsafe nano-TiO₂ and firmly supported MnO_x particles. Mn replaced noble metals such as Au or Ag, opening the way for the development of lower cost catalysts. Varying Mn loading or pH during the impregnation affected the final activity, thus giving important information to optimize the synthesis. Photocatalytic activity screening occurred on the gas-phase degradation of ethanol as a reference molecule, both under ultraviolet (UV) (6 h) and Light Emitting Diode (LED) (24 h) irradiation. Mn-doped TiO₂ reached a maximum ethanol degradation of 35% under visible light after 24 h for the sample containing 20% of Mn. Also, we found that an acidic pH increased both ethanol degradation and mineralization to CO₂, while an alkaline pH drastically slowed down the reaction. A strict correlation between photocatalytic results and physico-chemical characterizations of the synthesized powders were drawn.

Enhanced TiO2 nanorods photocatalysts with partially reduced graphene oxide for degrading aqueous hazardous pollutants

Enhanced TiO₂ nanorods (TNRs) with partially reduced graphene oxide (RGO) (designated as GT) were prepared for degrading aqueous hazardous pollutants. The degree of RGO oxidation had an important role in affecting the photoelectronic and photocatalytic activities of GT composites. The study examined the impact of the degree of RGO oxidation on the photocatalytic activities. The photocatalytic activity of the materials was investigated for degrading rhodamine b (RhB), methyl orange (MO), methylene blue (MB), and phenol by using ultraviolet (UV) light. The highest photocatalytic activity was observed when the atomic oxygen-to-carbon (O/C) ratio of RGO was 0.130 ± 0.003. This study suggested the photocatalytic performance was maximized by preserving a selected amount of the RGO oxygen-containing groups. The work reported in this study on optimizing the RGO-based TiO₂ photocatalyst could serve as a promising approach for preparing and optimizing other types of carbon-based photocatalysts such as graphene-based CdS.

Heterogeneous UV/Fenton degradation of bisphenol A catalyzed by synergistic effects of FeCo2O4/TiO2/GO

A new method for bisphenol A (BPA) degradation in aqueous solution was developed. The characteristics of BPA degradation in a heterogeneous ultraviolet (UV)/Fenton reaction catalyzed by FeCo₂O₄/TiO₂/graphite oxide (GO) were studied. The properties of the synthesized catalysts were characterized using scanning electron microscopy, X-ray diffraction, and vibrating sample magnetometry. FeCo₂O₄ and TiO₂ were grown as spherical shape, rough surface, and relatively uniform on the surface of GO (FeCo₂O₄/TiO₂/GO). Batch tests were conducted to evaluate the effects of the initial pH, FeCo₂O₄/TiO₂/GO dosage, and H₂O₂ concentration on BPA degradation. In a system with 0.5 g L^-1 of FeCo₂O₄/TiO₂/GO and 10 mmol L^-1 of H₂O₂, approximately 90 % of BPA (20 mg L^-1) was degraded within 240 min of UV irradiation at pH 6.0. The reused FeCo₂O₄/TiO₂/GO catalyst retained its activity after three cycles, which indicates that it is stable and reusable. The heterogeneous UV/Fenton reaction catalyzed by FeCo₂O₄/TiO₂/GO is a promising advanced oxidation technology for treating wastewater that contains BPA.