Photocatalytic Degradation Of Formic Acid Research Articles

Gold supported on graphene oxide/silica photocatalyst for hydrogen generation from formic acid

Hydrogen gas has attracted a great deal of attention as a fuel due to its non-polluting combustion reaction. A wide variety of approaches have been employed to generate this green fuel with a remarkable concentration on photocatalytic pathways, in which a free source of energy is consumed for hydrogen evolution. Accordingly, we focused on construction of a photocatalyst of gold supported on graphene oxide–silicon dioxide (SiO2) for hydrogen generation through photocatalytic degradation of formic acid. It was demonstrated that the modification of SiO2 with graphene oxide and gold surprisingly extended photo-absorption of the semiconductor. The nanocomposite productively consumed photoelectrons for conversion of protons to hydrogen with turnover frequency of 539 h−1 at room temperature. This high activity of the nanocomposite was ascribed to the formation of simultaneous electron-rich and hole-rich centers in interfaces of graphene oxide–gold and graphene oxide–SiO2, respectively, which accelerated the process by both hydrogen generation in electron-doped sites and CO2 evolution in hole-doped platforms.

Influence of Salts on the Photocatalytic Degradation of Formic Acid in Wastewater.

Conventional wastewater treatment technologies have difficulties in feasibly removing persistent organics. The photocatalytic oxidation of these contaminants offers an economical and environmentally friendly solution. In this study, TiO2 membranes and Ag/TiO2 membranes were prepared and used for the decomposition of dissolved formic acid in wastewater. The photochemical deposition of silver on a TiO2 membrane improved the decomposition rate. The rate doubled by depositing ca. 2.5 mg of Ag per 1 g of TiO2. The influence of salinity on formic acid decomposition was studied. The presence of inorganic salts reduced the treatment performance of the TiO2 membranes to half. Ag/TiO2 membranes had a larger reduction of ca. 40%. The performance was recovered by washing the membranes with water. The anion adsorption on the membrane surface likely caused the performance reduction.

Influence of the Micro-Nanostructuring of Titanium Dioxide Films on the Photocatalytic Degradation of Formic Acid under UV Illumination.

Surface micro-nanostructuring can provide new functionalities and properties to coatings. For example, it can improve the absorption efficiency, hydrophobicity and/or tribology properties. In this context, we studied the influence of micro-nanostructuring on the photocatalytic efficiency of sol-gel TiO2 coatings during formic acid degradation under UV illumination. The micro-nanostructuring was performed using the UV illumination of microspheres deposited on a photopatternable sol-gel layer, leading to a hexagonal arrangement of micropillars after development. The structures and coatings were characterized using Raman spectroscopy, ellipsometry, atomic force microscopy and scanning electron microscopy. When the sol-gel TiO2 films were unstructured and untreated at 500 °C, their effect on formic acid’s degradation under UV light was negligible. However, when the films were annealed at 500 °C, they crystallized in the anatase phase and affected the degradation of formic acid under UV light, also depending on the thickness of the layer. Finally, we demonstrated that surface micro-nanostructuring in the form of nanopillars can significantly increase the photocatalytic efficiency of a coating during the degradation of formic acid under UV light.

Low temperature design of titanium dioxide anatase materials decorated with cyanuric acid for formic acid photodegradation

The influence of cyanuric acid (CA) on the structural, textural, electronic, morphological properties and the photocatalytic activity of titanium dioxide materials (TNCA) were herein evaluated. TNCAs samples were prepared through the sol gel method. The novelty of this work that cyanuric acid; the so far most recalcitrant molecule, is used here as reservoir of nitrogen. The synthesis of TNCAs nanomaterials are performed at low temperature in presence of quaternary ammonium as co-catalyst for anatase growth. Samples were characterized by means of nitrogen adsorption-desorption isotherms at 77 K, X-ray diffraction (XRD), Infrared (ATR), Raman, diffuse reflectance ultraviolet-visible, photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopies, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photocatalytic activities of TNCAs and their free counterpart nanomaterials were then evaluated in the photocatalytic degradation of formic acid (FA) as model molecule under UV.X-ray and Raman show success of anatase phase formation at low temperature without any post-calcination. IR-ATR analysis confirms CA grafting onto TiO2 identified by formation of vibration band between Ti and triazine. SEM mapping shows that C, O, Ti, and N are homogeneously distributed in the nanomaterial. Nitrogen adsorption-desorption measurements at 77 K show developed textural properties; the heat of N2 adsorption seems to be affected by CA loading. PL and UV-visible spectroscopies show simultaneously (i) electron trapping by the oxygen vacancy identified by Raman spectroscopy by redshift of Eg1 mode and (ii) the hole is confined by nitrogen. Therefore, the excited electron can move from TiO2 VB to the new sublevels initiated by the introduction of nitrogen which results in quenching of the photoluminescence intensity. The photocatalytic activity of the various TNCAs nanomaterials increases versus CA loading. The highest kLH of TNCA2 (5 wt%) could be explained by short migration time conjugated with lower bulk recombination of the photogenerated electron hole.

Effect of dissolved silica on photocatalytic water purification with a TiO2 ceramic catalyst

If photocatalytic water purification technologies will find practical applications, the impact of total dissolved solids in the source water on the activity of the photocatalyst must be evaluated. In this study, we evaluated the effects of SiO32− in water on a TiO2 ceramic photocatalyst; specifically, we determined the effects of SiO32− on the rate of photocatalytic degradation of formic acid (as a model contaminant) and on the rate of photocatalytic inactivation of Escherichia coli in an aqueous solution. Both the rate of formic acid degradation and the sterilization rate decreased with increasing SiO32− concentration. On the other hand, at a given SiO32− concentration, the activity of the photocatalyst did not decrease over the course of 120 h, and the surface structure of the photocatalyst did not change (i.e., no precipitate formed on the surface). The decreases in photocatalytic activity due to the presence of SiO32− could be recovered by flushing the experimental apparatus with distilled water. These results show that the reason for the lower photocatalytic activity in the presence of SiO32− than in its absence was due to adsorption of SiO32− onto the surface of the TiO2 photocatalyst and that SiO32− adsorption was an equilibrium process in water.

Influence of reduced graphene oxide on the synergism between rutile and anatase TiO2 particles in photocatalytic degradation of formic acid

GO-TiO2 photocatalysts were prepared using titanium dioxide (TiO2) samples obtained by physical mixing of different amounts of anatase and rutile. The anatase/rutile mixtures were then supported by graphene oxide (GO) or reduced graphene oxide (rGO). The photocatalytic activity of these materials was investigated in the photodegradation of formic acid as a model reaction under UV/A light irradiation. (r)GO-TiO2 samples containing both anatase and rutile phases show higher activities than pure anatase, the maximum being reached with 88% anatase and 12% rutile. This synergism observed between anatase and rutile is amplified when graphene oxide is added, particularly under its reduced form. This enhancing effect was explained mainly in terms of electron transfer from anatase to rutile and then to graphene oxide or reduced graphene oxide. In this respect, partial reduction of graphene oxide appears as a remarkable way to avoid recombination of photogenerated electron-hole pairs. However, interestingly, the charge transfer is efficient only if rutile is present in TiO2 samples.

Reduced graphene oxide/TiO2 nanotube composites for formic acid photodegradation

The influence on the photocatalytic performance of TiO2 nanotubes (NT) resulting from the addition of graphene oxide (GO) was studied. TiO2 nanotubes (NT) were prepared using alkaline hydrothermal treatment of TiO2 P25 followed by calcination at 400°C under air. GO-NT composites were then obtained by wet impregnation of the as-prepared TiO2 nanotubes onto graphene oxide before reduction under H2 at 200°C. In a first step, the influence of the reduction treatment was evaluated on GO alone to determine its role towards the nature of the oxygen-containing functional groups present. GO-NT composites were also characterized considering both the effect of the reduction treatment and of the GO weight loading on textural, structural, electronic, and optical properties of TiO2 nanotubes. The resulting GO-NT composites were finally evaluated for the photocatalytic degradation of formic acid and compared to TiO2 nanotubes alone and to P25. Results emphasize a strong increase of the electron affinity and conductivity of the GO-NT composites if graphene oxide is reduced at 200°C. These enhanced properties lead to an easier separation of photogenerated charges and to a limitation of the recombination of electron-hole pairs. A dramatic gain in photocatalytic response is observed. Maximum in photocatalytic efficiency is reached at a GO loading of 1.0wt% while further increase of GO weight loading blocks light penetration and depletes the photocatalytic response.

Design of La–C60/TiO2 Nanocomposites: Study of the Effect of Lanthanum and Fullerenol Addition Order onto TiO2. Application for the Photocatalytic Degradation of Formic Acid

Abstract La–C60/TiO2 nanocomposites were successfully obtained by dry impregnation method. The effect of La and polyhydroxylated fullerenol C60(OH)n addition order onto TiO2 was carefully highlighted. Interesting photocatalytic activity was achieved for the material firstly added with lanthanum. The increase in photocatalytic activity is attributed mainly to the synergy between fullerenol and La. Fullerenol enhances the electron charge transfer; whereas La increases the TiO2 thermal stability by adjusting the TiO2 crystallites sizes to low values and also by creating some structural defects.

Effect of cerium content and post-thermal treatment on doped anisotropic TiO2 nanomaterials and kinetic study of the photodegradation of formic acid

In this work, the design of cerium doped TiO2 nanomaterials with tuned structural and textural properties is reported. The influence of the cerium content of doped TiO2 solids (x=1 to 5wt%) on the photocatalytic degradation of formic acid using UV-A light was evaluated.The best photocatalytic activity was reached for 1wt% of cerium.The effect of post-thermal treatments was also herein highlighted by varying the calcination temperature between 400°C and 700°C for simultaneously doped- and cerium-free TiO2 samples. Characterization was performed by means of nitrogen adsorption–desorption isotherms at 77K, X-ray diffraction, Raman spectroscopy, Photoluminescence (PL) spectroscopy, and diffuse reflectance UV–vis spectroscopy. The presence of Ce limits the growth of TiO2 crystallite sizes during the post-thermal treatment and favors stabilization of the TiO2 anatase phase. The presence of cerium also increases the number of surface defects and transforms them to non-radiative centers able to capture the photogenerated electrons as observed by PL spectroscopy. This would leave photogenerated holes available improving consequentlythe photocatalytic activity for the oxidation of formic acid. Finally, a possible pathway mechanism is proposed to confirm the obtained results.

The role of lanthanum in the enhancement of photocatalytic properties of TiO2 nanomaterials obtained by calcination of hydrogenotitanate nanotubes

The influence of lanthanum on the thermal stability and photocatalytic activity of calcined hydrogenotitanate nanotubes (HNT) was herein evaluated. HNT samples were prepared through the hydrothermal treatment of TiO2 P25 in a concentrated NaOH solution (11.25M) at 130°C during 20h followed by acid washing. La-doped titanates nanotubes (La–HNT) photocatalysts with optimum 1wt% of La were then elaborated by incipient wetness impregnation method using lanthanum nitrate as precursor. La–HNT and HNT samples were then calcined at temperatures varying between 400°C and 700°C. Samples were characterized by means of nitrogen adsorption–desorption isotherms at 77K, X-ray diffraction (XRD), Raman spectroscopy, diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL), transmission electron microscopy (TEM), ICP analysis and photocurrent experiments. The photocatalytic activities of La–HNT and HNT derived nanomaterials were then evaluated through the photocatalytic degradation of formic acid (FA).Main results reveal that lanthanum inhibits TiO2 crystallite growth and retards anatase transformation into the less active rutile phase. The addition of La ions to TiO2 results in a charge imbalance creating a high proportion of oxygen vacancies as evidenced by photocurrent, photoluminescence and Raman experiments.The photocatalytic experiments reveal that La-doped TiO2 helps to maintain a high photocatalytic activity level even after calcination at high temperatures contrary to La-free photocatalysts. The determination of kinetic parameters reveals that the maintaining of a high photocatalytic activity results from the synergetic effect between restriction of TiO2 crystallite size growth and formation of a high proportion of oxygen vacancies.

One step synthesis of N-doped and Au-loaded TiO2 nanoparticles by laser pyrolysis: Application in photocatalysis

Photocatalysis is a major tool for air and water depollution and photocatalysts with improved efficiency in the visible range are still needed. In this context, we show that N-TiO2 nanoparticles modified with Au, called Au/N-TiO2, seem to represent a good compromise: significant photocatalytic activity is observed under visible light together with an activity higher than TiO2 P25 under UV irradiation. In order to demonstrate such efficiency of the Au/N-TiO2 sample, TiO2, Au-TiO2, N-TiO2 and Au modified N-TiO2 nanoparticles were synthesized in one step using the laser pyrolysis method. The photocatalytic activity of the powders was evaluated through the photocatalytic degradation of formic acid (FA) both under UV and visible light irradiation. Under UV irradiation, all the laser-synthesized samples exhibit a high efficiency compared to commercial TiO2 P25. Moreover, the modification by Au induces an enhancement of the photocatalytic activity compared to pure TiO2 even at very low concentrations. Under visible light, the N-doped samples exhibit some photoactivity and the degradation rate of FA in presence of Au/N-TiO2 is much increased compared to N-TiO2. In conclusion, our Au/N-TiO2 sample exhibits efficiency better than P25 under UV together with an activity under visible light.

Design of TiO2 nanorods and nanotubes doped with lanthanum and comparative kinetic study in the photodegradation of formic acid

Lanthanum doped 1D-TiO2 nanomaterials (nanorods and nanotubes) with tuned structural and textural properties have been evaluated in the photocatalytic degradation of formic acid (FA) under UV conditions. La-doped nanorods and nanotubes calcined at 973K show interesting photocatalytic properties with respect to La-free nanomaterials. The presence of La inhibits TiO2 crystallite growth and increases the lifetime of photo-generated electron–hole pairs.

Design of TiO2 nanomaterials for the photodegradation of formic acid – Adsorption isotherms and kinetics study

1D-TiO2 nanomaterials (nanotubes, nanorods, nanoplates, nanospheres and nanoparticles) with tuned structural and textural properties have been evaluated in the photocatalytic degradation of formic acid (FA) under UV conditions. The FA adsorption isotherms follow the model of Langmuir and the kinetic of FA photodegradation shows Langmuir–Hinshelwood model whatever the TiO2 morphologies. TiO2 nanotubes (HTNT-400), nanoplates (HTNW-700) and nanoparticles (HTNT-500 and HTNT-600) show an interesting photocatalytic activities compared to TiO2 nanospheres (P25) and nanorods (TNR). The nanotubular TiO2 (HTNT-400) has a photocatalytic activity 4 times higher than TiO2 P25. The enhanced activity is attributed to the smaller crystallite size of anatase and tuned surface area of the photocatalyst. The pH study showed that the coexistence of HCOO− and HCOOH species at natural pH (ca. 3.5) is favourable for better adsorption on active sites of titanium oxide nanomaterials and consequently to a better photocatalytic activity.

Effect of Na content and thermal treatment of titanate nanotubes on the photocatalytic degradation of formic acid

The influence of the sodium content on thermal stability and photocatalytic activity of calcined titanate nanotubes (TNT) was herein evaluated by preparing different samples through hydrothermal treatment of TiO2 powder (P25) in a concentrated NaOH solution (11.25M) at 130°C during 20h followed by acid washing steps. Titanate nanotubes samples with sodium (Na-TNT) and sodium-free (H-TNT) were then obtained using different concentrations of HCl aqueous solutions namely 0.1M and 1M respectively. As synthesized nanomaterials with different Na percentages were then calcined at temperatures varying between 400°C and 700°C. Samples were characterized by means of nitrogen adsorption-desorption isotherms at 77K, thermal analysis (DTA, TGA), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and diffuse reflectance spectroscopy (DRS). The photocatalytic activities of Na-TNT and H-TNT derived nanomaterials were then evaluated through the photocatalytic degradation of formic acid (FA).Results show that the presence of sodium retards the dehydration process during the transformation of titanate into TiO2 shifting the formation of anatase phase to higher temperatures. However, sodium is not necessary to preserve the nanotubular morphology. The presence of sodium after calcination strongly impacts negatively the photocatalytic properties. If sodium is completely removed from the initial titanate orthorhombic phase, calcination leads to TiO2 anatase materials with enhanced photocatalytic properties compared to P25 in the degradation of formic acid, particularly if nanotubular morphology is preserved. The highest activity was therefore achieved for the H-TNT sample calcined at 400°C. The photodegradation activity of formic acid depends on the specific surface areas and TiO2 crystallinity. In pure anatase nanoparticles the activity strongly decreases with coherent crystallographic domains ≥10nm.

Photocatalytic activity of S- and F-doped TiO2 in formic acid mineralization

Two series of doped titanium dioxide samples (S-TiO(2) and F-TiO(2)) were prepared by the sol-gel method in the presence of different amounts of dopant source (thiourea and NH(4)F, respectively), followed by calcination at 500, 600 or 700 °C, and characterised by BET, UV-vis absorption, XPS, HRTEM, XRD and EPR analyses. Reference undoped materials were prepared by the same synthetic procedure. Their photocatalytic activity under visible light was investigated employing the photocatalytic degradation of formic acid in aqueous suspension as test reaction. S-doped TiO(2) showed a photocatalytic activity quite similar to that of undoped materials. In this regard, the insertion of S, characterised by a relatively large ionic radius, into the TiO(2) crystalline structure appears rather difficult, as confirmed by XPS analysis. On the contrary, moderate F doping was beneficial in increasing the rate of formic acid photocatalytic degradation, especially for photocatalysts calcined at high temperature, consisting of highly crystalline pure anatase, in which the rate of detrimental charge carrier recombination was reduced. For both series of doped materials, high doping levels appear to limit the semiconductor photoactivity, probably due to the formation of a progressively increasing number of charge recombination centres. The EPR characterisation of the investigated doped TiO(2) samples evidenced the presence of nitrogen containing species (nitric oxide radical encapsulated in micro-void, with no photoactivity, and N(b)˙ species, active in visible light sensitisation) and of titanium reduced centres Ti(3+), due to charge imbalance consequent to dopant introduction in the TiO(2) lattice either in anionic (F(-)) or in cationic form (S(6+)).

Synthesis of Al-substituted mesoporous silica coupled with CdS nanoparticles for photocatalytic generation of hydrogen

Aluminum-substituted mesoporous silica (Al-HMS) molecular sieve coupled with CdS nanoparticles (CdS/Al-HMS) were prepared by template assembly, ion-exchange and sulfuration routes. The XRD and TEM results indicated that the assembly of less than 2 wt% CdS nanoparticles in the porous channels of Al-HMS didn't significantly affect the wormhole-like mesoporous framework structure of Al-HMS, whereas the porous channels of Al-HMS were filled up by CdS nanoparticles after loading of 21 wt% CdS. The diffuse reflectance UV–visible spectra exhibited that the absorption edge was gradually blue-shifted with decrease in CdS content due to the quantum confinement effect. The CdS/Al-HMS sample loaded 0.99 wt% Ru showed the highest H 2 evolution at a rate of 13.23 mL h −1 with an apparent quantum yield of 5.92% at 420 nm by photocatalytic degradation of formic acid under visible light irradiation.

Photocatalytic degradation of formic acid with simultaneous production of hydrogen over Pt and Ru-loaded CdS/Al-HMS photocatalysts

The CdS/Al-HMS, Pt- and Ru-loaded CdS/Al-HMS photocatalysts were prepared by template, ion exchange and precipitation reaction, and were characterized by N 2 adsorption/desorption measurements, X-ray diffraction (XRD), UV–Visible diffuse reflectance spectra (UVDRS), X-ray fluorescence (XRF), transmission electron microscopy (TEM) and fluorescence emission spectra (FES). The result showed that CdS in the form of clusters was highly dispersed inside the channels of Al-HMS. The reaction activities of photocatalysts were examined by photocatalytic degradation of formic acid under visible light irradiation ( λ ≥ 420 nm). The photocatalyst, CdS/Al-HMS loaded 0.34 wt.% Pt, showed the highest H 2 evolution at a rate of 7.63 mL h − 1 with an apparent quantum yield of 2%.

Preparation of Ru-loaded CdS/Al-HMS nanocomposites and production of hydrogen by photocatalytic degradation of formic acid

The composite of aluminum-substituted mesoporous silica (Al-HMS) molecular sieve coupled with CdS (CdS/Al-HMS) was prepared by template, ion exchange and sulfurization reactions. The result of low angle XRD patterns showed that the low content of 2.5 wt% CdS is incorporated inside Al-HMS channels. The results of diffuse reflectance UV–visible spectra and fluorescence emission spectra exhibited that the absorption edge and photoluminescence peak for CdS/Al-HMS are blue-shifted about 75 nm and 40 nm in comparison to bulk CdS, respectively. The activities of hydrogen production by photocatalytic degradation of formic acid were evaluated under visible light irradiation ( λ ≥ 420 nm) and the CdS/Al-HMS loaded 0.07 wt% Ru showed the highest H 2 evolution at a rate of 3.7 mL h −1 with an apparent quantum yield of 1.2% at 420 nm.

Predictive radiation field modeling for fluidized bed photocatalytic reactors

A predictive model of the radiation distribution for fluidized bed photocatalytic reactors was proposed and solved by means of the Monte Carlo approach coupled with the ray tracing technique. This model considers the interaction between the photocatalytic TiO 2 -coated spheres and the photons, taking into account the shadowing effect of the beads, the reflection on the surface of the spheres, and the absorption in the TiO 2 films. This radiation model is completely predictive and does not use any adjustable parameter. Modeling results indicate a strong influence of the bed expansion on the radiation distribution, with the shadowing effect of the beads being the main cause for this dependence. Increasing the bed expansion improves the uniformity of the radiation distribution in the reactor. Nevertheless, an excessively expanded bed would reduce the efficiency of the reactor because the transmittance of the bed increases and a fraction of photons leave the reactor without being absorbed by the TiO 2 -coated spheres. The radiation model was evaluated in a laboratory-scale fluidized bed photocatalytic reactor that was designed and built for the elimination of organic pollutants from water streams. TiO 2 -coated glass spheres with a diameter of 1.18 mm were used as photocatalyst. The model was validated by comparing the predicted values of the effective transmittance of the bed with experimental results measured under different bed expansions. The performance of the reactor was also assessed experimentally, showing a good efficiency for the photocatalytic degradation of formic acid as a model compound.

A new kinetic model of photocatalytic degradation of formic acid in UV/TiO2 suspension system with in-situ monitoring

The results show that a newly developed kinetic model can successfully explain the photocatalytic kinetics of formic acid in UV/TiO2 suspension system with in-situ monitoring and the apparent rate constant (k) is affected by the initial concentrations of formic acid, amounts of TiO2, UV intensity and pH.