Photocatalytic Efficiency Of TiO2 Research Articles

Facile and rapid synthesis of solar-driven TiO2/g-C3N4 heterostructure photocatalysts for enhanced photocatalytic activity

TiO2 has been successfully coupled with graphitic carbon nitride (g-C3N4) using the thermal deposition method to create an advanced heterojunction photocatalyst. The prepared photocatalysts were studied for photocatalytic hydrogen production and methylene blue dye degradation. The synthesized materials were thoroughly characterized by XRD, XPS, FT-IR, HR-TEM, UV-Vis DRS, and Photoluminescence studies. The results obtained clearly confirm that the photocatalytic efficiency of TiO2 is significantly enhanced after making the nanocomposite with g-C3N4 nanostructures. The hydrogen production rate under simulated sunlight irradiation for a TiO2/g-C3N4 heterojunction photocatalyst has been obtained at approximately 110 μmolg−1h−1. Trapping tests of active species during photocatalysis clearly revealed that O2•‒ played a critical role to enhance the activity. It is significantly proved that the enhancement in the photocatalytic activity is due to the interfacial contact between the TiO2 and g-C3N4, which effectively reduces the electron hole recombination. Eventually, the influence of bandgap energies and their band edge potentials were discussed by proposing a well defined schematic mechanism.

Performance characterization of a hybrid adsorptive-photocatalytic (APC) oscillatory membrane reactor for micropollutant removal

• Hybrid adsorptive-photocatalytic (APC) oscillatory membrane reactor was tested. • Up to ∼ 2.5 fold increase in diclofenac (DCF) removal was achieved using APC. • Performance of APC reduced only after continuous operation of 100 h. • The operational cost of the APC was estimated ∼ 2.2–4.4 $/m 3 . In order to reduce the operating cost and plant footprint, process intensification (PI) of tertiary treatment technologies is needed for recycling various effluents. In this study, the performance of a hybrid adsorptive-photocatalytic (APC) oscillatory membrane reactor was characterized by quantifying the degradation/ removal of diclofenac (DCF) as a model pollutant. The intensification effect is achieved through the synergy of a hybrid photocatalysis, activated carbon (AC) adsorption and membrane separation combined with flow modulation in a single unit. Commercial TiO 2 nanoparticles were used as a photocatalyst, while AC was immobilized onto a stainless steel (SS) mesh beneath microfiltration (MF) membrane, were used as pollutant adsorption and separation media, respectively. Initially, the individual effect of AC adsorption and photocatalysis on the reactor performance was quantified and subsequently, the combined effect of AC adsorption and slurry photocatalysis in the hybrid configuration was evaluated. In addition, a degradation pathway for DCF removal was proposed. The APC configuration provided significant process enhancement with up to ∼ 2.5 fold increase in DCF removal compared to the removal obtained using AC adsorption or photocatalysis alone. The electrical energy per unit order (EEO) for the process was estimated as ∼ 2.2–4.4 $/m 3 . A decline in system performance was noticed after extended hours of continuous operation (∼100 h) mainly due to saturation of AC coating and decrease in photocatalytic efficiency of TiO 2 due to formation of degradation byproducts. Both the smaller footprint of the design combined with the hybrid configuration and flow modulation can provide an effective PI approach for tertiary treatment for water recycling.

A Simple and Ligand‐Free Synthesis of Light and Durable Metal‐TiO2 Polymer Films with Enhanced Photocatalytic Properties

AbstractThe photocatalytic efficiency of TiO2 can be increased by using co‐catalysts, such as metal nanoparticles, which act as electron sinks to suppress the recombination of photogenerated electron–hole pairs. The main challenge in preparing such systems is to create intimate contact between the metal and the TiO2 surface while still maintaining control over the morphology and distribution of the metal nanoparticles in the TiO2 matrix. Here lightweight TiO2 films are prepared by assembling a layer of TiO2 nanoparticles onto a thin polymer support, followed by physical vapor deposition of metal nanoparticles onto the TiO2 surface. Importantly the fabrication does not involve any chemical modifications to the surface of NPs, which allows spontaneous formation of strong chemical bonds between deposited metal and TiO2. Systematic optimization of this process gives materials 6× more catalytically active than the parent TiO2 films and up to 18× more catalytically active than commercial photoactive TiO2 glass. Moreover, the transparent, flexible, and robust polymer support enables the product films to be easily used for repeated photocatalytic reactions. Since the whole fabrication process is scalable and highly reproducible, this approach provides new opportunities for controlled synthesis of a new family of practical high‐performance metal‐ semiconductor hybrid photocatalysts.

Synthesis and Characterization of Enhanced Photocatalytic Activity with Li+-Doping Nanosized TiO2 Catalyst.

The photocatalytic efficiency of TiO2 is reduced by rapid electron–hole recombination. An effective approach to address this limitation is to have TiO2 doped with various metal ions or heteroatoms. Herein, we prepared a series of Li+-doped TiO2 nanoparticles showing high photocatalytic activities through the sol–gel method. The samples were characterized by X-ray diffraction (XRD) and surface area analyses. Effects of Li+ doping on the Brunauer–Emmett–Teller (BET) surface area, crystallite size, phase transformation temperature, and phase composition were studied. The results showed that Li+ doping can promote the generation of the rutile crystal phase in TiO2, lower the anatase-to-rutile transformation temperature, and generate the mixed-crystal effect. The photocatalytic degradation of methyl orange (MO) was used as a probe reaction to evaluate the photoactivity of the nanoparticles. Parameters affecting the photocatalytic efficiency, including the Li+ doping amount, calcination temperature, and catalyst amount, as well as the kinetics of the photocatalytic process toward the degradation of MO, were investigated. The mixed-crystal TiO2, which was doped with 1.0 mol % Li+ and calcined at 550 °C containing 27.1% rutile and 72.9% anatase phase, showed a 2.2-fold increase in the photoactivity on the basis of the rate constant of MO decomposition as compared with the undoped TiO2. The existence of a definite quantity of rutile phase could effectively inhibit the recombination of the electron–hole pairs, thus promoting photocatalytic activity.

Controlled formation of Ag-AgxO nanoparticles on the surface of commercial TiO2 based composites for enhanced photocatalytic degradation of oxalic acid and phenol

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.

TiO2-coated 2D photonic crystals for reflectometric determination of malachite green.

A "detect and destroy" strategy is reported for the spectroscopic determination and photocatalytic degradation of Malachite Green (MG) in aqueous solutions. The intensity of the reflection peak maxima from the TiO2-coated 2D-photonic crystal (PhC) at 633nm wavelength undergoes a gradual decrease with increasing concentrations of MG. The determination of MG was readily achieved in thenanomolar range due to the quenching of the reflection intensity of the peak, measured using a fiber optic probe. The assay works in the 1.0 nM to 10μM MG concentration range with a detection limit of 1.3 nM. The same TiO2-coated 2D-PhC surface can photocatalytically degrade MG in aqueous solutions under UV irradiation. The photocatalytic degradation in the presence of TiO2-coated 2D-PhC becomes evident as the blue color of MG changes to colorless with increasing irradiation time. The decrease in absorption is detected at 617nm. It was found that the photocatalytic efficiency of TiO2 was synergistically enhanced in the presence of 2D-PhCs. It is concluded that each component of theTiO2-coated 2D-PhCsystem plays a key role in the detection and degradation of MG. Graphical abstractSchematic representation for reflectometric detection and photocatalytic degradation of hazardous Malachite Green dye using TiO2-coated two-dimensional photonic crystals.

Adhesive-free in situ synthesis of a coral-like titanium dioxide@poly(phenylene sulfide) microporous membrane for visible-light photocatalysis

Nanosized titanium dioxide (TiO2)-based materials are regarded as an effective approach for disposing organic pollutants. However, their wide bandgap, rapid electron/hole recombination, poor chemisorption, and aggregation limit their photoactivity and photocatalytic efficiency. In this study, the coupling of TiO2 and a conjugated polymer membrane is created to improve the photoactivity and photocatalytic efficiency of TiO2. Nanosized TiO2 with high crystallinity is synthesized on the surface of the pretreated poly(phenylene sulfide) (PPS) porous membrane through the in situ hydrothermal process. Strong interaction forms between the prepared TiO2 and the membrane matrix, which leads to the efficient migration and transfer of electron-hole pairs. As a result, the band gap and the electron/hole recombination rate of TiO2 significantly decrease. The TiO2@PPS membrane possesses better adsorption capacity compared with the photocatalyst consisting of individual TiO2, which will greatly increase the photocatalytic efficiency. Various dyes can be degraded almost completely after being irradiated for 90 min under visible light. In a word, it may provide a facile approach for preparing a photocatalytic membrane with a high catalyst loading amount, a large chemisorption capacity, and high visible-light photoactivity.

Plasmon-enhanced photocatalysis: Ag/TiO2 nanocomposite for the photochemical reduction of bicarbonate to formic acid

ABSTRACTPlasmonic metallic nanoparticles can significantly enhance the catalytic efficiency of semiconductors via plasmonic photocatalysis. In this study, a hybrid Ag/TiO2 photocatalyst was synthesized and tested for the photochemical reduction of bicarbonate to value-added formic acid. It was found that under solar irradiation, TiO2 is not very efficient, but formate production is significantly increased with the addition of silver nanoparticles. Under 365 nm irradiation, the photocatalytic efficiency of TiO2 is enhanced, but no effect was observed with the addition of silver nanoparticles. Under solar irradiation, Ag/TiO2 reached an apparent quantum efficiency (AQE) of 7.78 ± 0.04%, the highest AQE observed so far. Enhanced photocatalytic activity is attributed to the synergistic effect between UV photon excitation of TiO2 and surface plasmon resonance enhancement. To elucidate the mechanism of plasmon-enhanced photocatalysis, experiments were performed under solar irradiation and 365 nm irradiation. We propose that photo-excited electrons are transferred from above the Fermi level of the metal nanoparticle to the conduction band of the semiconductor through plasmon-induced electron transfer.

Hydrothermal synthesis of Mo-C co-doped TiO2 and coupled with fluorine-doped tin oxide (FTO) for high-efficiency photodegradation of methylene blue and tetracycline: Effect of donor-acceptor passivated co-doping

Limited by the narrow photoresponse range and high electron-hole recombination rate, the photocatalytic efficiency of TiO2 is still far below what is expected. Herein, the Mo-C donor-acceptor passivated co-doping TiO2 ((Mo,C)-TiO2) was synthesized via a hydrothermal synthetic strategy, then it is coupled with FTO. The donor-acceptor co-doped TiO2 exhibit band gap reduction of ∼1.0 eV, and enable the nanoparticles to be photoactive in the visible light range. The band structure investigated by Mott-Schottky plots and valence band spectra reveal that doping induces an extended-tail-states near the valence band edges, which is responsible for the photoresponse in the visible light region. Density-functional theory (DFT) calculations manifest that donor-acceptor co-doping TiO2 exhibit both the advantages of the Mo, C mono-doped cases, and results in higher charge density in (Mo,C)-TiO2. The photoluminescence (PL) spectra and time-resolved PL spectra show that co-doping induced deep electron trap state in (Mo,C)-TiO2, confirmed by the surface photovoltage (SPV) spectroscopy, which enables accumulate long-lived photoinduced electrons and effectively suppresses the radiative electron-hole recombination. Meanwhile, FTO as the electronic receiver is beneficial for the charge carrier separation. As expected, the (Mo,C)-TiO2/FTO photocatalysts show a remarkably enhanced photocatalytic activity in the visible-light irradiation degradation of methylene blue (MB) and tetracycline (TC), up to ∼4 times higher than that of TiO2.

Assessment of the Photocatalytic Efficiency of TiO<sub>2</sub> in the Presence of Sulphate

The use of salts on the degradation of toxic substances may cause the acceleration or delay of radicals production originating from the degradation process. This work had as its objective to investigate the presence and absence of potassium sulphate salt on the photocatalysis of Bentazone using TiO2 as a catalyzer. The effect of the sulphate ion on the photodegradation of the Bentazone herbicide was studied using concentrations of 0,05; 0,10 and 0,20 g L-1 with 0,5 g L-1 of TiO2, in suspension of 180 mL from bentazone solution (3,0x10-5 mol L-1). The samples were analyzed through UV-Vis spectroscopy. The presence of sulphate ions presented a difference of 3,3% on the degradation of bentazone in comparison to TiO2 alone.

Synthesis of Nb doped TiO2 nanotube/reduced graphene oxide heterostructure photocatalyst with high visible light photocatalytic activity

Limited by the narrowed photoresponse range and unsatisfactory recombination of photoinduced electron-hole pairs, the photocatalytic efficiency of TiO2 is still far below what is expected. Here, we initially doped TiO2 nanotubes (TNTS) by transition metal ion Nb, then it is coupled with reduced graphene oxide (rGO) to construct a heterostructure photocatalyst. The defect state presented in TiO2 leading to the formation of localized midgap states (MS) in the bandgap, which regulating the band structure of TiO2 and extending the optical absorption to visible light region. The internal charge transport and transfer behavior analyzed by electrochemical impedance spectroscopy (EIS) reveal that the coupling of rGO with TNTS results in the formation of electron transport channel in the heterostructure, which makes a great contribution to the photoinduced charge separation. As expected, the Nb-TNTS/rGO exhibits a stable and remarkably enhanced photocatalytic activity in the visible-light irradiation degradation of methylene blue (MB), up to ∼5 times with respect to TNTS, which is attributed to the effective inhibition of charge recombination, the reduction of bandgap and higher redox potential, as well as the great adsorptivity.

Photocatalytic Efficiency of TiO2-Biomass Loaded Mixture for Wastewater Treatment

The objective of this study was to assess the efficiency of a novel TiO2/modified sago bark (TiO2/MSB) mixture for the degradation of sago wastewater effluent by employing response surface methodology (RSM) using chemical oxygen demand (COD) removal as the target parameter. The highest COD removal of 64.92% was obtained using TiO2/MSB mixture sample prepared by combining 0.2 g/L TiO2and 1 w/w% MSB. Given that the highest removal was produced using this mixture sample, further optimisation of sago wastewater treatment was conducted by varying the independent variables, namely, dosage and contact time. Under this optimum condition, 0.10 g of 0.2 g/L TiO2/1% MSB had successfully reduced 52.83% COD in 120 min. Surface morphology, functional groups, and elemental analysis supported observations of the ability of TiO2/MSB mixture to remove COD. Additionally, aeration had further improved COD removal by 11%. The regression value (R2>0.99) of the model indicated a high degree of correlation between the evaluated parameters. These results proved the feasibility of TiO2photocatalysis as an appealing alternative protocol for sago wastewater treatment and solid waste from the industry can be utilised for wastewater degradation.

Effect of ytterbium doping concentration on structural, optical and photocatalytic properties of TiO2 thin films

Abstract Ytterbium (Yb) doped TiO 2 thin films have been synthesized by sol-gel spin-coating technique. Films with different Yb concentrations such as 0.5, 1, 2, 4 wt% were deposited and the impact of the dopant concentration on their physicochemical properties was evaluated. The films were characterized by X-Ray diffraction, transmission electron microscopy, Raman spectroscopy, UV–Vis transmittance spectroscopy and photoresponse. The results showed that the incorporation of ytterbium modified the properties of TiO 2 films. The photocatalytic efficiency of TiO 2 :Yb films was determined using methylene blue (MB) as the generic pollutant. Compared to undoped TiO 2 , 1 wt% Yb doped films exhibited higher photocatalytic activity toward MB degradation under UV light. When the amount of Yb dopant concentration was increased, there was a negative effect on the photosensitivity and photocatalysis.

Preparation and photocatalytic property of Ce3+-doped titanium dioxide nanotubes

ABSTRACTTo enhance the photocatalytic efficiency of TiO2, different concentration of Ce3+-doped TiO2 nanotubes were prepared using a sol-gel method combined with a hydrothermal process. After being calcined at 450°C, the morphology, composition, and crystal structures were investigated by SEM, TEM, XRD, and EDS. The samples' photocatalytic performance was characterized by degrading methylene blue under illumination of a 250 W UV-light. The result showed that both ends of the nanotubes were ringent and consisted of many layers. Their length could reach to hundred nanometers and the thickness of the walls was about 9 nm. The low-concentration Ce3+ did not influence the nanostructure and crystal structure but has a large correlation with the photocatalytic efficiency. The sample with the concentration of 1.5% performed best in photocatalytic reaction.

Using Titanium Dioxide/carbon Nanotubes To Remove Humic Acids In Water

This study used multi-walled carbon nanotubes (MWCNTs), TiO2 and their mixture (TiO2/CNT) to remove humic acids (HA) in water. The thermodynamic parameters with respect to the adsorption of MWCNTs, including free energy of adsorption (ΔG 0 ), enthalpy (ΔH 0 ), and entropy (ΔS 0 ) changes, are further calculated in the study. The ΔH 0 data showed the adsorption of HA onto MWCNTs is an endothermic physisorption. The ΔG 0 data indicates the adsorption of HA onto MWCNTs was spontaneous and thermodynamically favorable. Photocatalytic experiments showed 60 mgl -1 of HAs were completely degraded and mineralized as CO2 after 5 h UV irradiation by 0.8 gl -1 of TiO2, indicating the efficiency of TiO2 for the removal of HA is better than CNTs. The experiments of TiO2/CNT indicated the photocatalytic efficiency of TiO2 in the presence of CNTs was not improved, even worse than TiO2 alone. However, the photocatalytic efficiency of TiO2/CNT mixture became better than TiO2 alone due to the supply of oxygen by aeration, ascribing to the reason that the provided oxygen might be adsorbed on the

Treatment of Dye Wastewater Using Hydrothermally Prepared Nano-TiO2 Under Natural Light

Nano-TiO2 material was prepared with Ti(OC4H9)4 and C2H5OH, using hydrothermal method. Then nano-TiO2 was calcined at high temperature and its catalytic activity for the degradation of dye wastewater under simulated natural light was measured. After that the crystal structure of nano-TiO2 was characterized by XRD, TEM and BET. Experimental results show that the volume ratio of water to alcohol, hydrothermal time, calcination temperature and the amount of ester used have significant effects on the photocatalytic efficiency of TiO2. When nano-TiO2 was prepared under the conditions with a volume ratio of water to alcohol of 1:3, hydrothermal time of 4 h and calcination temperature at 500 °C, its photocatalytic efficiency was the best. The degradation of reactive yellow solution can reach above 74 % in 180 min.

Photocatalysis of Volatile Organic Compounds in water: Towards a deeper understanding of the role of cyclodextrins in the photodegradation of toluene over titanium dioxide

HypothesisCyclodextrin-assisted photodegradation of toluene was investigated in water in the presence of a photo-irradiated commercial titanium dioxide photocatalyst. It was expected that cyclodextrins could form water-soluble supramolecular host/guest complexes with the toluene and thus promote the approach of the pollutant on the TiO2 surface and enhance the phototocatalytic oxidation efficiency. ExperimentsPhotodegradation kinetics of toluene were investigated under UV-C and near-visible light radiation in aqueous suspensions of TiO2. Impact of cyclodextrin (CD) on the photocatalytic efficiency of TiO2 was evaluated with different cyclodextrins: α-CD, β-CD, γ-CD and RAME-β-CD. Host–guest association constants were determined by static headspace gas chromatography and affinity of cyclodextrins for the TiO2 surface by isothermal adsorption studies. Issue of the cyclodextrin stability during the degradation process was examined using Total Organic Carbon, NMR and MALDI-TOF analyses. FindingsToluene could be fully mineralized by TiO2 in water within hours, even if the presence of cyclodextrin caused a delay in the photodegradation process. The chemical nature of cyclodextrins was found to exert a significant influence on the extent of inhibitory effect, which was discussed in terms of balance between solubilization efficiency, substrate protection and coverage of active sites of TiO2 by competitive adsorption. The cyclodextrin degradation was also studied and discussed.

Theoretical and experimental studies on N, Fe, La co-doped anatase TiO2 band adjustment

Based on the plane wave method (PWPP) of densiy functional theory (DFT) we model the N, Fe, La three elements co-doped anatase TiO2 crystal structure and calculate its band structure and density of states with Material Studio. By the sol-gel method, the intrinsic anatase TiO2 and the anatase TiO2 with N, Fe, La three elements co-doping are prepared and investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). Results indicate that the changes of the N, Fe, La co-doped TiO2 lattice volume and its bond length will result in a decline of the crystal symmetry and the effective separation of the electron-hole pair. Impurity level appearing at the bottom of the conduction band and at the top of valence band leads to the decrease of the TiO2 forbidden band width(1.78 eV to 1.35 eV, reduced by 25%), the red shift of light absorption edge, the increase of density of states as well as, the improve ment of electron transition probability and the photocatalytic efficiency of TiO2. Ion doping makes the particles in doped TiO2 become smaller, i.e. the size of particles in TiO2>N/Fe_TiO2>N/Fe/La_TiO2, the emission peak of the N/Fe/La: TiO2 is 425 nm and its energy gap is smaller than that of the intrinsic TiO2. The measured N/Fe/La: TiO2 photocatalytic ability is stronger than the N/Fe: TiO2, the origin can be due to the increasing number of the electronic states and the impurity energy levels.

Effects of Sn Ion on Photocatalytic Performances of Titanium Dioxide Thin Film

In order to improve the photocatalytic efficiency of TiO2, through adding different concentration of Sn ion, the photocatalytic performances of TiO2 thin films are changed. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) spectrum of TiO2 thin films before and after doping Sn ion are compared, and the transmission spectrum and optical absorption spectrum of TiO2 thin film are analyzed. The results show that: after the implantation of Sn ion, there is a new compound Ti1-xSnxO2 on the TiO2 film’s surface, which has a higher photocatalytic activity than pure TiO2. In addition, Sn/TiO2 film has broaden the scope of its light response after ion implantation, so that it can be more effectively in using light source to send out the photons of longer waveband, and makes the photocatalytic activity of Sn/TiO2 thin films increase.

Preparation of Photocatalyst of Nano-TiO<sub>2</sub> Coating on SiO<sub>2</sub> Carrier and its Photocatalytic Activity

The photocatalytic efficiency of TiO2 can be significantly improved by loading TiO2 on adsorption carriersSiO2 gel beads. The novel photocatalytic reagents can adsorb organic matters around the semiconductor particles, enhance the local concentration, prevent the intermediates from volatilizing and drifting away, and accelerate the reaction. The supporters depended on the micro-cystic cavity made of surfactant, sodium dodecyl sulfate and sodium silicate, aggregation spherical SiO2 colloidal particles taking sodium silicate as matrix, prepares TiO2/SiO2 catalyst by absorbing anatase TiO2 on the surface of hydroxide silicon. Characterization of the catalyst by SEM and XRD, and the photocatalytic activity through the degradation rate of humic acid are investigated. The experiments demonstrated that: the molar ratio of sodium silicate to sodium dodecyl sulfate (SDS) is 3/5 and the molar ratio of TiO2 to SiO2 is 1/8, the particle size of prepared catalyst is 0.5-30μm, and the TiO2/SiO2 catalyst showed ideal performance of adsorption and photocatalytic activity.