Photocatalytic Oxidation Of Organic Compounds Research Articles

Modeling of UV-LED photocatalytic reactors for the degradation of gaseous volatile organic compounds (VOCs) in indoor environments

A computational model was developed to predict the photocatalytic oxidation of organic compounds in an ultraviolet light-emitting diode (UV-LED) reactor. To simulate the overall reactor performance, the fluid flow, mass transfer, radiation, and kinetics were modeled and integrated by solving the governing equations of mass, momentum, species, and radiant energy conservation, using computational fluid dynamics (CFD) software. The kinetic parameters were experimentally measured and were defined in the model. The model could reliably predict the reactor’s performance and was in close agreement with the experiments within the range of studied photocatalyst orientation, flowrates (Re = 1125 – 36000), and ultraviolet (UV) irradiances (Iavg = 1.4 – 13.8 mW/cm2). Our results revealed that toluene, as the model organic compound, can effectively diffuse to the catalyst surface resulting in minimal mass transfer limitation (less than 4%) even at the lowest examined flow rate (Re = 1125). The experimental data and simulation results both showed close-to-zero mass transfer limitation at the turbulent flow regime (Re≥ 4600). The modeling results identified the areas of the highest mass transfer limitation using the local values of velocity and concentration. The developed model can be applied to the virtual prototyping as well as design and optimization of UV-LED air purification reactors.

Enhanced Photocatalytic Activity Using Near Visible Light of ZnO Nanorods by Doping with Mn2+ Ions

ZnO is a promising photocatalyst for photocatalytic oxidation of organic compounds under the influence of sunlight that provides clean energy and decomposes sustainable organic pollutants substances. ZnO is found to have non-toxic properties, long-term stability, high carrier mobility, low cost and biocompatibility. However, some disadvantages of ZnO limit its use in photocatalysis. Due to its wide bandgap, ZnO can only be activated under UV illumination. On the other hand, the photo-excited electron-hole pairs that recombine quickly on ZnO surface, suppress its photocatalytic properties. To improve its properties and performance, doping with transition metals was used to improve the optical properties of ZnO. Among the transition metal ions, Manganese (Mn) was commonly used to improve and tune the optical, electrical, diameter, height, and the number of nanorods (NRs) per unit area. Introduction of Mn into ZnO could enhance the photocatalytic activity due to the increase in the defect sites that effectively decreased the recombination of free electrons and holes. This study successfully synthesized ZnO nanorod arrays generated on glass substrates with different concentrations of doping Mn (0, 0.5, 1, 1.5 and 2%) at 100 °C by a simple hydrothermal method. To investigate the structure, morphology and optical properties, ultraviolet-visible spectroscopy (UV-Vis), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were conducted. With the range of Mn doping ≤ 2% mol, the band gap reduced slightly, and the most optimized Mn doping concentration was of 0.5%. Overall, this work shows that the most effective way to increase ZnO’s photocatalytic activity in the visible region by reducing its band gap was the reduction in the size of the material or denaturation of ZnO by certain metals or non-metals.

9,10-Dihydroanthracene auto-photooxidation efficiently triggered photo-catalytic oxidation of organic compounds by molecular oxygen under visible light

The development of mild and efficient process for the selective oxidation of organic compounds by molecular oxygen (O2) can be one of the key technologies for synthesizing oxygenates. This paper discloses an efficient and mild synthesis protocol for the O2-involved ethylbenzene (EB) photooxidation triggered by 910-dihydroanthracene (DHA) auto- photooxidation in acetone under visible light illumination, which can achieve 87.7 % EB conversion and 99.5 % acetylacetone (ACP) selectivity under ambient conditions. Also, 62.9 % EB conversion and 96.3 % ACP selectivity is obtained in air atmosphere. Furthermore, this protocol has a good adaptability for the photooxidation of other organic substrates such as tetrahydronaphthalene, diphenylmethane, toluene, cyclohexane, cyclohexene, alcohol, methylfuran and thioether to their corresponding oxygenates. A series of control and quenching tests, combined with EPR spectra, suggest that the photo-excited DHA can transfer its photo-electron to O2 to yield a superoxide radical anion (O2⚫−), then DHA is preferentially oxidized to anthraquinone (AQ) by the active O2⚫− owing to its high reactivity. Finally, the in situ generated AQ as an active photo-catalyst can achieve the photooxidation of EB and other organic compounds by O2. The present photo-autoxidation protocol gives a good example for the O2-based selective oxidation of inert hydrocarbons under mild conditions.

Novel Pd-loaded urchin-like (NH4)xWO3/WO3 as an efficient visible-light-driven photocatalyst for partial conversion of benzyl alcohol

Photocatalytic oxidation of organic compounds by solar light is a promising strategy for environmentally benign conversion processes. Herein, we first report an urchin-like Pd/(NH4)xWO3/WO3 with three-dimensional hierarchical microstructure prepared through a thiourea-assisted solvothermal method followed by calcination under the reductive atmosphere. The Pd/(NH4)xWO3/WO3 exhibits higher selectivity in comparison to Pd/WO3 nanorods in the partial conversion of aqueous benzyl alcohol into benzaldehyde (e.g., 80% selectivity for benzaldehyde production with ca. 84% conversion of benzyl alcohol) under visible light irradiation. The preferential generation of hydroxyl radicals from water on the (NH4)xWO3/WO3 surface in the initial reaction stage was responsible for the high selectivity for benzaldehyde production because hydroxyl radicals react with benzyl alcohol much more efficiently than benzaldehyde. DFT calculations demonstrate that the energy barrier of the reaction between benzyl alcohol and hydroxyl radicals largely decreased due to the photo-excited triplet states of (NH4)xWO3/WO3, while such a trend in the energy barrier was not observed for other photocatalysts. On the other hand, with extended irradiation time, a large amount of hydrogen peroxide, which was produced by the multi-electron reduction of oxygen molecules, accumulates on the Pd/(NH4)xWO3/WO3 due to the low activity of the Pd cocatalyst. The generated hydrogen peroxide preferentially eliminated the photoexcited holes when the concentrations of benzaldehyde increased, thus inhibiting the peroxidation of benzaldehyde by holes. The Pd/(NH4)xWO3/WO3 may provide a feasible strategy for the photocatalytic oxidation of various other organic compounds due to its unique reactivity shown in this study.

Novel PCS Output Calibration Technique

Many issues like large size, poor response time and accuracy which were plaguing the performance of the conventional Photo Catalytic Processes were overcome by PCS (Photo Catalytic Sensor). The continuing advancements in the field of sensor interface development are to calibrate and correct the inherent non-idealities present in transducers forced us to work in this area. The varieties of different parameters inside PCS subject to the transfer characteristics of PCS results because of Photo-catalytic oxidation of organic compounds has been done by Whig and Ahmad in 2015 and it is found that the major contributors to non-idealness are typically the nonlinear response to stimulus (gain), the temperature, and the offset dependence of either of these elements. Expectedly the calibration of the sensor has been done physically in the research facility available in laboratory before the genuine deployment in the system. This requires a great deal of manual calculation very high skilled manpower. To make this tedious procedure easy and to make PCS sensor more accurate, a novel sensor calibration with built-in calibration registers using FPGAs is proposed.

Anaerobic Alcohol Conversion to Carbonyl Compounds over Nanoscaled Rh-Doped SrTiO3 under Visible Light.

Photocatalytic oxidation of organic compounds on semiconductors provides a mild approach for organic synthesis and solar energy utilization. Herein, we identify the key points for the photocatalytic oxidation over Pt-loaded Rh-doped strontium titanate allowing the conversion of alcohols efficiently and selectively to aldehydes and ketones under anaerobic conditions and visible light with an apparent quantum efficiency of pure benzyl alcohol oxidation at 420 nm of ≤49.5%. Mechanistic investigations suggest that thermodynamically the controlled valence band edge position via Rh doping provides a suitable oxidation ability of photogenerated holes, avoiding the powerful hydroxyl radical intermediates prone to overoxidation resulting in high selectivity. Kinetically, oxygen vacancies induced by Rh3+ substitution in the SrTiO3 lattice not only favor the dissociative adsorption of alcohols yielding alkoxy species but also induce the weakening of the α-C-H bond facilitating its cleavage by the photogenerated holes. Pt nanoparticles deposited as a cocatalyst contribute to the final hydrogen evolution.

Preparation of a shell nanostructure for highly selective photocatalytic oxidation of organic compounds by wrapping on NiO nanorods exposed {110} facets with ultrathin g-C3N4 nanosheets

Semiconductor building blocks of varying dimensionality have been used to prepare multifunctional heterostructural photocatalysts that can efficiently separate photo-generated carriers to enhance photocatalytic activity, while exposing the desired reactive facets of the semiconductor via structure engineering remains a fascinating strategy. In this work, ultrathin graphitic‑carbon nitride (g-C3N4) nanosheets (NSs) and NiO nanorods (NRs) with exposed {110} facets were utilized as assembly units to strategically construct well-defined g-C3N4@NiO heterostructure via a facile self-assembly, and g-C3N4 NSs were uniformly and intimately enwrapped on the NiO NRs. This shell nanostructure possessed remarkably high photocatalytic activity in the oxidation of organic compounds and in photoelectrochemical reactions. The underlying reasons accounting for the considerably improved photocatalytic oxidation performances of g-C3N4@NiO heterostructure were examined, which resulted from the more efficient charge separation/transfer thanks to the peculiar structural merits of g-C3N4 NSs and NiO NRs, as well as from the intimate interfacial contact and unique spatial integration mode between them. The predominant active species in the photocatalytic oxidation were determined unambiguously, which enabled to elucidate the mechanism of the photocatalytic oxidation.

Charge carrier trapping, recombination and transfer during TiO2 photocatalysis: An overview

Heterogeneous photocatalysis mediated by semiconducting TiO2 has attracted continuous interest during the past decades and has shown great potentials in environmental remediation and solar energy conversion. Basically, photocatalysis is initiated by the TiO2 excitation. The generated charge carriers undergo trapping, recombination, and interfacial transfer before proceeding the redox reaction at TiO2 surface. Monitoring the charge carrier dynamics is of particulate importance for understanding the underlying mechanism and designing efficient photocatalysts. This review overviews the recent progress in characterization of charge carrier dynamics. We will present the analytic techniques for monitoring the fate of charge carriers at each elementary photocatalytic step, including charge carrier generation, trapping and recombination inside the photocatalyst, as well as the interfacial charge transfer. The charge carrier dynamics at TiO2/H2O interface, hole transfer reactions for O2 production, and photocatalytic oxidation of organic compounds and nitric oxides, and electron transfer reactions for photocatalytic reduction of viologens and metal ions are addressed, aiming at a deeper understanding of photocatalytic process.

Preparation of Ti species coating hydrotalcite by chemical vapor deposition for photodegradation of azo dye

TiO2 in anatase crystal phase is a very effective catalyst in the photocatalytic oxidation of organic compounds in water. To improve its photocatalytic activity, the Ti-coating MgAl hydrotalcite (Ti–MgAl–LDH) was prepared by chemical vapor deposition (CVD) method. Response surface method (RSM) was employed to evaluate the effect of Ti species coating parameters on the photocatalytic activity, which was found to be affected by the furnace temperature, N2 flow rate and influx time of precursor gas. Application of RSM successfully increased the photocatalytic efficiency of the Ti–MgAl–LDH in methylene blue photodegradation under UV irradiation, leading to improved economy of the process. According to the results from X-ray diffraction, scanning electron microscopy, Brunner–Emmet–Teller and Barrett–Joyner–Hallender, thermogravimetric and differential thermal analysis, UV–vis diffuse reflectance spectra analyses, the Ti species (TiO2 or/and Ti4+) were successfully coated on the MgAl–LDH matrix. The Ti species on the surface of the Ti–MgAl–LDH lead to a higher photocatalytic performance than commercial TiO2-P25. The results suggested that CVD method provided a new approach for the industrial preparation of Ti-coating MgAl–LDH material with good photocatalytic performances.

Ti(iv) nanoclusters as a promoter on semiconductor photocatalysts for the oxidation of organic compounds

Ti(IV) clusters act to accelerate the photocatalytic oxidation of organic compounds.

Photocatalytic oxidation of organic compounds in a hybrid system composed of a molecular catalyst and visible light-absorbing semiconductor.

Photocatalytic oxidation of organic compounds proceeded efficiently in a hybrid system with ruthenium aqua complexes as catalysts, BiVO4 as a light absorber, [Co(NH3)5Cl](2+) as a sacrificial electron acceptor and water as an oxygen source. The photogenerated holes in the semiconductor are used to oxidize molecular catalysts into the high-valent Ru(IV)=O intermediates for 2e(-) oxidation.

A rotating disk study of the photocatalytic oxidation of p-nitrophenol on phosphorus-modified TiO2 photocatalyst

After discussing the general aspects of photocatalytic oxidation of organic compounds in aqueous solutions and the application of the rotating disk theory to (photo)catalytic phenomena, we report the oxidation of p-nitrophenol (PNP) on illuminated phosphorus modified TiO2 (P-TiO2) and TiO2 photocatalysts under controlled hydrodynamic conditions. We found that the performance of the oxygen transfer reaction can be described considering mass transport in solution and surface reaction according to Langmuir–Hinshelwood kinetics. From analysis of the dependence of the reaction rate on the rotation rate, we obtained the apparent organic–photocatalyst adduct interaction constant K, the rate constant k of the surface reaction between adsorbed PNP and hydroxyl radicals, and the diffusion coefficient D of PNP in solution. The results showed that degradation of PNP using P-TiO2 and UV light was readily possible, with reaction half-lives significantly lower than those obtained using pristine TiO2 photocatalyst.

Controllable synthesis of Cu2O/Cu composites with stable photocatalytic properties.

Here we reported a facile approach to synthesize Cu2O/Cu composite particles by one-step sono-chemical process. The content of Cu in the Cu2O/Cu composites can be easily controlled by adjusting the synthesis time. Phase, morphology and optical properties of the products were carried out by X-ray diffraction (XRD), field-emission scanning electron microscopy (FSEM), transmission electron microscope (TEM), ultraviolet-visible (UV-vis) spectroscopy and nitrogen adsorption apparatus. Using photocatalytic degradation of Methyl orange (MeO) dye under visible-light illumination, we have investigated the influence of Cu on the photocatalytic activity of Cu2O, to find out its potential application in waste water treatment. Especially, the stability of the photocatalyst was confirmed using reclaimed Cu2O/Cu in ten successive runs. Results demonstrated clearly that Cu2O/Cu were stable and resistant to photocorrosion during the photocatalytic oxidation of organic compounds, indicating that these Cu2O/Cu composites are promising candidates for pollutant processing.

Decomposition of rhodamine 6G in the presence of titania coupling coupled with carbon source as photocatalyst under visible light excitation

Heterogeneous photocatalytic degradation of N-containing R6G dye was achieved by visible light-activated carbon doped TiO2 (C-TiO2) nanoparticles, synthesized by a low-temperature wet-chemical technique using glucose as carbon source. The structural and physicochemical properties of C-TiO2 were characterized by X-ray diffraction (XRD), Raman spectroscopy, UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and FT-IR spectroscopy. Compared with the pure TiO2, the carbon modified nanomaterials exhibited enhanced absorption in the broad visible-light region together with an apparent red shift in the optical absorption edge. The resulting carbon-doped TiO2 catalyst was employed as an effective photocatalyst for degradation of Rhodamine 6G (R6G) in aqueous solutions under visible light irradiation (λ > 420 nm). In addition, the intrinsic mechanism of visible light-induced photocatalytic oxidation of organic compounds on the carbon-doped titania was proposed and discussed.

Non-Current-Field Induced Photocatalysis: Efficient Enhancement of Photooxidation of Organic Compounds with TiO2 Film Electrodes

Using field induced surface photovoltage spectroscopy (FISPS) and photocatalysis, the effect of non-current field induction on photocatalysis has been studied. Enhancement has been observed for the photocatalytic oxidation of organic compounds (phenol as a model molecule) with TiO2 film electrodes under non-current field. With this technique, photocatalysis displays an efficient, power-saving and stable performance. The FISPS technique has been developed to explain some of the experimental observations. It is concluded that the effect of non-current field induction on photocatalysis is mainly due more efficient charge separation resulting in an increase in surface photovoltage.

Angulated Bi3+–WO3 with Significant Alkali Resistance and Efficient Photocatalytic Activity

Abstract Angulated WO3 modified with Bi3+ (Bi–WO3) showed very high resistance to 1 M NaOH solution. Moreover, the activities of Pt/Bi–WO3 both before and after immersion in NaOH solution were excellent for the photocatalytic oxidation of organic compounds under visible light.

Kinetic enhancement in photocatalytic oxidation of organic compounds by WO3 in the presence of Fenton-like reagent

WO3-mediated photocatalytic oxidation is achievable in the presence of electron acceptors as an alternative to O2 or co-catalysts enabling O2 reduction pathway. This study suggests the combination with Fenton-like reagent (Fe(III)/H2O2) as a strategy to improve the photocatalytic activity of WO3. Under neutral pH condition where Fe(III) is present as iron oxide precipitate, photocatalytic degradation of 4-chlorophenol (4-CP) proceeded 3-fold faster in the WO3/Fe(III)/H2O2 system relative to the WO3/H2O2 system, while no noticeable oxidation occurred in the systems of Fe(III)/H2O2, WO3, and WO3/Fe(III). Such efficacy increase at circumneutral pH was observed in photocatalytic oxidation of diverse organics including phenol, bisphenol A, acetaminophen, and carbamazepine. Compatible with the pH dependence of photocatalytic activity of the WO3/Fe(III)/H2O2 system, hydroxylation of benzoic acid and coumarin as indirect indication for OH radical production was drastically retarded with increasing pH. The pH effect indicates that OH radical as primary oxidant may be responsible for the kinetic enhancement in the WO3/Fe(III)/H2O2 system. In that platinum deposits or Nafion layers as physical barriers possibly inhibit surface Fe(III) precipitation, use of platinized or Nafion-coated WO3 caused the negligible photocatalytic improvement in the ternary system. Effective oxidative degradation in the presence of the UV cut-off filter corroborated visible light activation of the WO3/Fe(III)/H2O2 system.

Photocatalytic Oxidation of Organic Compounds in Water by Using Ruthenium(II)–Pyridylamine Complexes as Catalysts with High Efficiency and Selectivity

The photocatalytic oxidation of organic substrates such as alcohols was conducted in the presence of RuII–aqua complexes as oxidation catalysts, [RuII(bpy)3]2+ as a photosensitizer and electron mediator, and a CoIII complex as a sacrificial oxidant (see scheme). The catalytic systems exhibited high efficiency to achieve turnover numbers of over 8000.

Degradation of Humic Acid Using a CdS/TiO<sub>2</sub> Nanotubes Electrode

Use NH4F as the electrolyte, prepared TiO2 nanotubes which orderly arranged by anodic oxidation. CdS was load to the TiO2-nanotubes by using chemical deposition method, then controlled size of CdS particles and uniformly load had been found when the EDTA-2NA was mixed in. The structure and morphology of TiO2 nanotubes and modified TiO2 nanotubes were observed by SEM. Use humic acid as simulate pollutant, investigate the efficiency of the CdS / TiO2nanotubes photocatalytic oxidation of organic compounds .The results show that CdS modified TiO2nanotubes arrays after added EDTA-2NA, the degradation rate of humic acid increased from 57.1 % to 85.4 % after illumination.

Visible light-induced photocatalysis through surface plasmon excitation of platinum-metallized titania for photocatalytic bleaching of rhodamine B

Nanocomposites consisting of titania nanoparticles and metallic platinum were prepared via a soft chemical reduction method. The detailed structural, compositional, and optical characterization and physicochemical properties of the obtained products were analyzed by X-ray diffraction, nitrogen adsorption, Raman spectroscopy, UV–Vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, and FT-IR spectroscopy techniques. Employing photodegradation of rhodamine B as the model reaction, we found that the as-prepared Pt/TiO2 nanocomposite showed an excellent photocatalytic oxidation activity under visible light irradiation. On the basis of these results, the intrinsic mechanism of visible light-induced photocatalytic oxidation of organic compounds on the platinized titania is proposed and discussed. The superior visible light-driven photocatalytic efficiency of the Pt/TiO2 nanocomposite photocatalyst can be ascribed to the high efficiency of charge-pair separation due to the presence of deposited Pt serving as electron sinks to retard the rapid e−–h+ couple recombination; the good photoabsorption capacity in the visible light region; and the higher concentration of surface hydroxyl groups, which are able to effectively scavenge photogenerated valence band holes. Accumulation of the holes at the catalyst surface increases the probability of the formation of OH· as a reactive species that readily oxidizes the organic dye molecule.