Enhancement of Visible-Light Photocatalytic Degradation of Tetracycline by Co-Doped TiO2 Templated by Waste Tobacco Stem Silk.

In this study, Co-doped TiO2 was synthesized using waste tobacco stem silk (TSS) as a template via a one-pot impregnation method. These samples were characterized using various physicochemical techniques such as N2 adsorption/desorption analysis, diffuse reflectance UV-visible spectroscopy, X-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, and electron paramagnetic resonance spectroscopy. The synthesized material was used for the photodegradation of tetracycline hydrochloride (TCH) under visible light (420-800 nm). No strong photodegradation activity was observed for mesoporous TiO2 synthesized using waste TSS as a template, mesoporous Co-doped TiO2, or TiO2. In contrast, Co-doped mesoporous TiO2 synthesized using waste TSS as a template exhibited significant photocatalytic degradation, with 86% removal of TCH. Moreover, owing to the unique chemical structure of Ti-O-Co, the energy gap of TiO2 decreased. The edge of the absorption band was redshifted, such that the photoexcitation energy for generating electron-hole pairs decreased. The electron-hole separation efficiency improved, rendering the microstructured biotemplated TiO2 a much more efficient catalyst for the visible-light degradation of TCH.

Cobalt and sulfur co-doped nano-size TiO2 for photodegradation of various dyes and phenol.

Various compositions of cobalt and sulfur co-doped titania nano-photocatalyst are synthesized via sol-gel method. A number of techniques including X-ray diffraction (XRD), ultraviolet-visible (UV-Vis), Rutherford backscattering spectrometry (RBS), thermal gravimetric analysis (TGA), Raman, N2 sorption, electron microscopy are used to examine composition, crystalline phase, morphology, distribution of dopants, surface area and optical properties of synthesized materials. The synthesized materials consisted of quasispherical nanoparticles of anatase phase exhibiting a high surface area and homogeneous distribution of dopants. Cobalt and sulfur co-doped titania demonstrated remarkable structural and optical properties leading to an efficient photocatalytic activity for degradation of dyes and phenol under visible light irradiations. Moreover, the effect of dye concentration, catalyst dose and pH on photodegradation behavior of environmental pollutants and recyclability of the catalyst is also examined to optimize the activity of nano-photocatalyst and gain a better understanding of the process.

Preparation and photocatalytic application of terbium and sulfur co-doped titanium nanomaterials.

Titanium-based nanomaterials co-doped with terbium (Tb) and sulfur (S) were synthesized by sol-gel method via a facile step. Physicochemical properties of the resulting composites were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), X-ray photo-electron spectroscopy (XPS) and UV-Vis diffused reflectance spectroscopy (DRS). Methylene blue (MB) was used as a degradation target for evaluating the photocatalytic performance. The factors which influence the photocatalytic activity were investigated, including calcined temperatures and S doping amount. Tb, S (2 wt%) co-doped TiO2 composite calcined at 500 °C exhibited the highest photocatalytic activity with a degradation rate of 72.4% in 3 h. The reaction constant was 0.11529, 0.26025, 0.35038 and 0.41462 h-1 for undoped TiO2, Tb-doped TiO2, S-doped TiO2 and Tb, S co-doped TiO2, respectively. Importantly, the synergistic effect of terbium and sulfur dopants was profoundly discussed. Furthermore, recycling tests and acute toxicity experiments were carried out to confirm the reusability and biosafety of Tb, S co-doped TiO2.

Enhanced visible light photoelectrocatalytic degradation of tetracycline hydrochloride by I and P co-doped TiO2 photoelectrode.

Elimination of antibiotics such as tetracycline hydrochloride (TC) from wastewater is of great significance, but still faces challenges. Herein, for the first time, I and P co-doped TiO2 catalysts were prepared via a hydrolysis method. We also reported a simple method to prepare I and P co-doped TiO2 photoelectrodes, which exhibited preeminent photoelectrocatalytic (PEC) performance for the decomposition of TC. The synergistic effect of I and P co-doping could significantly improve the charge separation rate and enhance the light absorption capacity of TiO2, leading to an enhancement of PEC activity. The main factors affecting the PEC performance were investigated, and the highest degradation rate constant (4.20 × 10-2 min-1) was achieved when the doping content of P was 4 at% (ITP-4 photoelectrode) at pH 11.02 under visible light. The Langmuir-Hinshelwood kinetic model and active species trapping experiments were selected to investigate the degradation mechanism of TC. The results suggest that the hydroxyl radicals and photogenerated holes were the main active species that were responsible for the decomposition of TC. Moreover, the degradation pathways of TC based on the intermediates also demonstrated that the hydroxyl radicals and holes showed a principal role in degrading TC.

Preparation, characterization, and photocatalytic activity under UV and visible light of Co, Mn, and Ni mono-doped and (P,Mo) and (P,W) co-doped TiO2 nanoparticles: a comparative study.

In this work, TiO2-based nanomaterials have been successfully synthesized by doping TiO2 with Co, Mn, and Ni and by co-doping it with (P,Mo) or (P,W). The structural, optical, and morphological properties of the synthesized nanomaterials have been investigated using various techniques such as XRD, FTIR spectroscopy, UV-vis diffuse reflectance spectroscopy, XPS, and SEM-EDS. The obtained results showed that the crystalline structure of the doped TiO2-based nanomaterials depends strongly on the nature of the doping ions. The obtained band gap energy of TiO2 co-doped with (P,Mo) changes to a level below the band gap energy of TiO2 anatase indicating a high ability to absorb visible light. The obtained photocatalytic activity results of methyl orange degradation showed that, under visible light, the mono-doping of TiO2 with Co and its co-doping with (P,Mo) or (P,W) improve significantly the photocatalytic activity of TiO2 in comparison with undoped TiO2. The activity order obtained under UV-A irradiation for the used photocatalysts is TiO2 > > 1%Ni-TiO2 > 1%Co-TiO2 > 30%(P,Mo)-TiO2 ≈ 30%(P,W)TiO2 > 1%Mn-TiO2 while under visible light, it is 1%Co-TiO2 > 30%(P,Mo)-TiO2 > 30%(P,W)TiO2 ≈ TiO2 > 1%Ni-TiO2 > 1%Mn-TiO2. The high photocatalytic activity observed for these samples could be the result of a synergetic effect of the high visible light absorption capacity and the low recombination rate of photoexcited electrons and holes.

Adsorption-photocatalytic degradation and kinetic of sodium isobutyl xanthate using the nitrogen and cerium co-doping TiO2-coated activated carbon.

At present, the excessive use of sodium isobutyl xanthate (SIBX) in mineral processing has caused serious environmental problems, drawing ever-growing concern in China. A nitrogen and cerium co-doped TiO2-coated activated carbon (Ce/N-TiO2@AC) heterojunction were prepared through the sol-gel method to address these problems. The photocatalyst was characterized using XRD, TEM, SEM-EDS, PL, UV-Vis, XPS and a series of photoelectrochemical techniques. The results show that Ce/N-TiO2@AC photocatalyst possess a stable anatase phase, narrow band gap energy (2.24-2.61 eV) and high charge transport process. The photocatalytic activity of the photocatalyst was evaluated based on photodegradation kinetic studies of SIBX in aqueous solution, and it is found that it followed the Langmuir-Hinshelwood model very well. The Ce/N-TiO2@AC photocatalyst with 2% Ce appears to be the highest removal rate with 96.3% of SIBX and an apparent rate constant of 78.4 × 10-3 min-1. The reusability experiment for its potential applications was studied, and the removal rate of SIBX reached 95.8% after the fifth cycle. Besides, the proposed mechanism and degradation routes of SIBX were systematically studied, and certificate the concentration of SO2-4 ions in the final water sample was 95.9 mg/L, which was basically consistent with the theoretical value.

The Photocatalytic and Antibacterial Performance of Nitrogen-Doped TiO2: Surface-Structure Dependence and Silver-Deposition Effect.

Catalysts for visible-light-driven oxidative cleaning processes and antibacterial applications (also in the dark) were developed. In order to extend the photoactivity of titanium dioxide into the visible region, nitrogen-doped TiO2 catalysts with hollow and non-hollow structures were synthesized by co-precipitation (NT-A) and sol-gel (NT-U) methods, respectively. To increase their photocatalytic and antibacterial efficiencies, various amounts of silver were successfully loaded on the surfaces of these catalysts by using a facile photo-deposition technique. Their physical and chemical properties were evaluated by using scanning electron microscopy (SEM), transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDS), Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction (XRD), and diffuse reflectance spectra (DRS). The photocatalytic performances of the synthesized catalysts were examined in coumarin and 1,4-hydroquinone solutions. The results showed that the hollow structure of NT-A played an important role in obtaining high specific surface area and appreciable photoactivity. In addition, Ag-loading on the surface of non-hollow structured NT-U could double the photocatalytic performance with an optimum Ag concentration of 10-6 mol g-1, while a slight but monotonous decrease was caused in this respect for the hollow surface of NTA upon increasing Ag concentration. Comparing the catalysts with different structures regarding the photocatalytic performance, silverized non-hollow NT-U proved competitive with the hollow NT-A catalyst without Ag-loading for efficient visible-light-driven photocatalytic oxidative degradations. The former one, due to the silver nanoparticles on the catalyst surface, displayed an appreciable antibacterial activity, which was comparable to that of a reference material practically applied for disinfection in polymer coatings.

Effective La-Na Co-Doped TiO2 Nano-Particles for Dye Adsorption: Synthesis, Characterization and Study on Adsorption Kinetics.

The mesoporous La-Na co-doped TiO2 nanoparticles (NPs) have been synthesized by non-aqueous, solvent-controlled, sol-gel route. The substitutional doping of large sized Na+1 and La+3 at Ti4+ is confirmed by X-ray diffraction (XRD) and further supported by Transmission Electron Microscopy (TEM) and X-ray Photo-electron Spectroscopy (XPS). The consequent increase in adsorbed hydroxyl groups at surface of La-Na co-doped TiO2 results in decrease in pHIEP, which makes nanoparticle surface more prone to cationic methylene blue (MB) dye adsorption. The MB dye removal was examined by different metal doping, pH, contact time, NPs dose, initial dye concentration and temperature. Maximum dye removal percentage was achieved at pH 7.0. The kinetic analysis suggests adsorption dynamics is best described by pseudo second-order kinetic model. Langmuir adsorption isotherm studies revealed endothermic monolayer adsorption of Methylene Blue dye.

Chitosan modified N, S-doped TiO2 and N, S-doped ZnO for visible light photocatalytic degradation of tetracycline.

N, S-doped TiO2 (NST), N, S-doped ZnO (NSZ) and their composite with chitosan (NST/CS, NSZ/CS) were synthesized by sol gel-hydrothermal method. The prepared samples were characterized using XRD, FTIR, TEM and BET techniques. These photocatalysts were used for the photocatalytic degradation of tetracycline under visible light irradiation. At screening test, NST/CS had the highest tetracycline degradation efficiency of 91% for duration of 20 min under visible light. The blending of chitosan with NST increases the rate of photocatalytic degradation of tetracycline about 2 times. A detail characterization including HRTEM, SEM, EDS and DRS were conducted for NST/CS, the most active photocatalyst in this study. Photocatalytic activity test was conducted by varying tetracycline concentration, irradiation time, catalyst's concentration and pH using response surface methodology to find out the optimum condition for photocatalytic activity. The reusability of as-synthesized NST/CS was assessed which due to its high recoverability can be applied as an effective catalyst for degradation of organic substances in water and wastewater especially for degradation of emerging pollutants such pharmaceutical pollutants. The results from this work show a promising material for local authorities and pharmaceutical facilities to use for the treatment of pharmaceutical pollutants and tetracycline removal in water resource.

PAMAM templated N,Pt co-doped TiO2 for visible light photodegradation of brilliant black.

This study examined the photocatalytic degradation of an azo dye brilliant black (BB) using non-metal/metal co-doped TiO2. N,Pt co-doped TiO2 photocatalysts were prepared by a modified sol-gel method using amine-terminated polyamidoamine dendrimer generation 0 (PG0) as a template and source of nitrogen. Structural, morphological, and textural properties were evaluated using scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy (SEM/EDX), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA), Fourier transform infrared (FTIR), Raman spectroscopy (RS), photoluminescence (PL) and ultra-violet/visible spectroscopy (UV-Vis). The synthesized photocatalysts exhibited lower band gap energies as compared to the Degussa P-25, revealing a red shift in band gap towards the visible light absorption region. Photocatalytic activity of N,Pt co-doped TiO2 was measured by the reaction of photocatalytic degradation of BB dye. Enhanced photodegradation efficiency of BB was achieved after 180-min reaction time with an initial concentration of 50 ppm. This was attributed to the rod-like shape of the materials, larger surface area, and enhanced absorption of visible light induced by N,Pt co-doping. The N,Pt co-doped TiO2 also exhibited pseudo-first-order kinetic behavior with half-life and rate constant of 0.37 and 0.01984 min-1, respectively. The mechanism of the photodegradation of BB under the visible light irradiation was proposed. The obtained results prove that co-doping of TiO2 with N and Pt contributed to the enhanced photocatalytic performances of TiO2 for visible light-induced photodegradation of organic contaminants for environmental remediation. Therefore, this work provides a new approach to the synthesis of PAMAM templated N,Pt co-doped TiO2 for visible light photodegradation of brilliant black.

Fabrication of Ce/N co-doped TiO2/diatomite granule catalyst and its improved visible-light-driven photoactivity.

Eliminating antibiotic remnants in aquatic environment has become one of the hottest topics among current research works. Thus, we prepared Ce, N co-doped TiO2/diatomite granule (CNTD-G) catalyst to provide a new method. As one typical antibiotics, oxytetracycline (OTC) was selected as the target pollutant to be degradated under visible light irradiation. The carrier diatomite helped the spread of TiO2 nanoparticles onto its surface, and inhibited their agglomeration. The synergy of Ce and N dopants highly improved the visible-light-driven photoactivity of TiO2. The optimal doping amount and degradation conditions were determined. Besides, the effects of impurity ions were also investigated, including cations: Ca2+, Mg2+; or anions: NO3-, SO42- and PO43-. The intermediates generated during degradation process were studied, and the mechanism of the photodegradation process was proposed. CNTD-G could be easily collected from the reactor, and showed excellent recyclability.

Solvothermal syntheses of Bi and Zn co-doped TiO2 with enhanced electron-hole separation and efficient photodegradation of gaseous toluene under visible-light.

This study investigated the effects of Bi doped and Bi-Zn co-doped TiO2 on photodegradation of gaseous toluene. The doped TiO2 with various concentration of metal was prepared using the solvothermal route and characterized by SEM, XRD, Raman, BET, DRS, XPS, PL and EPR. Their photocatalytic activities under visible-light irradiation were drastically influenced by the dopant content. The results showed that moderate metal doping levels were obviously beneficial for the toluene degradation, while high doping levels suppressed the photocatalytic activity. The photocatalytic degradation of toluene over TiBi1.9%O2 and TiBi1.9%Zn1%O2 can reach to 51% and 93%, respectively, which are much higher than 25% of TiO2. Bi doping into TiO2 lattice generates new intermediate energy level of Bi below the CB edge of TiO2. The electron excitation from the VB to Bi orbitals results in the decreased band gap, extended absorption of visible-light and thus enhances its photocatalytic efficiency. Zn doping not only further enhances the absorption in this visible-light region, but also Zn dopant exists as the form of ZnO crystallites located on the interfaces of TiO2 agglomerates and acts as a mediator of interfacial charge transfer to suppress the electron-hole recombination. These synergistic effects are responsible for the enhanced photocatalytic performance.

Synergistic Effects of Sm and C Co-Doped Mixed Phase Crystalline TiO2 for Visible Light Photocatalytic Activity.

Mixed phase TiO2 nanoparticles with element doping by Sm and C were prepared via a facile sol-gel procedure. The UV-Vis light-diffuse reflectance spectroscopy analysis showed that the absorption region of co-doped TiO2 was shifted to the visible-light region, which was attributed to incorporation of samarium and carbon into the TiO2 lattice during high-temperature reaction. Samarium effectively decreased the anatase-rutile phase transformation. The grain size can be controlled by Sm doping to achieve a large specific surface area useful for the enhancement of photocatalytic activity. The photocatalytic activities under visible light irradiation were evaluated by photocatalytic degradation of methylene blue (MB). The degradation rate of MB over the Sm-C co-doped TiO2 sample was the best. Additionally, first-order apparent rate constants increased by about 4.3 times compared to that of commercial Degusssa P25 under the same experimental conditions. Using different types of scavengers, the results indicated that the electrons, holes, and •OH radicals are the main active species for the MB degradation. The high visible-light photocatalytic activity was attributed to low recombination of the photo-generated electrons and holes which originated from the synergistic effect of the co-doped ions and the heterostructure.

Enhanced performance of dye-sensitized solar cells aided by Sr,Cr co-doped TiO2 xerogel films made of uniform spheres.

One-pot preparation of Sr,Cr co-doped TiO2 xerogel film for boosting the short circuit current density of dye-sensitized solar cells (DSCs) is reported. The 2.5-µm-diameter spheres are assembled from 60nm nanoparticles by a modified sol-gel method. X-ray photoelectron spectroscopy (XPS) shows that Sr(2+) and Cr(3+) ions to be well incorporated into the titania crystal lattice without forming specific strontium and chromium compositions. The crystallite size, phase composition, and band structure of the particles depend on the dopants concentration. Isolated energy levels near valence band as a result of the transition ion (i.e., Cr) introduction, in conjunction with the local lattice distortions owing to the alkaline earth ion (i.e., Sr) insertion, improves the photocatalytic activity of the prepared TiO2 spheres, enhancing the short circuit current density of the cells. The DSC co-doped with 0.075 at.% Sr and 2.5 at.% Cr (i.e., S7C25 solar cell) showed the highest power conversion efficiency of 7.89% and short circuit current density of 18.58mA/cm(2) thanks to lower charge transfer resistance (2.35Ωcm(2)), lower electron transit time (1.26ms), and higher electron diffusion coefficient (17.1×10(4)cm(2)S(-1)) compared to the other cells, demonstrated by electrochemical impedance spectroscopy (EIS). The concept of simultaneously introduction of alkaline earth ions and transition ions into TiO2 lattice will open up a new insight into the fabrication of high performance DSCs.

Ultrasonic-assisted sol-gel synthesis of samarium, cerium co-doped TiO2 nanoparticles with enhanced sonocatalytic efficiency.

In this work, pure TiO2 and samarium, cerium mono-doped and co-doped TiO2 catalysts were synthesized by an ultrasonic-assisted sol-gel method and their sonocatalytic efficiency studied toward removal of Methyl Orange as a model organic pollutant from the textile industry. The relationship of structure and sonocatalytic performance of catalysts was established by using various techniques, such as XRD, TEM, SEM, EDX, DRS, and PL. A comparison on the removal efficiency of sonolysis alone and sonocatalytic processes was performed. The results showed that the samarium, cerium co-doped TiO2 catalyst with narrower band gap energy and smaller particle size leads to a rapid removal of pollutant. It was believed that Sm(3+) and Ce(4+) ions can serve as superficial trapping for electrons at conduction band of TiO2 and prolonged the lifetime of electron-hole pairs. Finally, the effect of synthesis and operational variables on the sonocatalytic activity of co-doped TiO2 catalyst was studied and optimized using response surface methodology as a statistical technique. The results showed that the maximum removal efficiency (96.33%) was achieved at the optimum conditions: samarium content of 0.6 wt%, cerium content of 0.82 wt%, initial pollutant concentration of 4.31 mg L(-1), catalyst dosage of 0.84 mg L(-1), ultrasonic irradiation power of 700 W, and irradiation time of 50 min.